A screw is a shaft with a helical groove or thread formed on its surface and provision at one end to turn the screw. A helix (pl helixes or helices) from the Greek word έλιξ, is a special kind of Space curve, i A screw thread is a helical or tapered structure used to convert between rotational and linear movement or force Its main uses are as a threaded fastener used to hold objects together, and as a simple machine used to translate torque into linear force. A fastener is a Hardware device that mechanically joins or affixes two or more objects together In Physics, especially Mechanics, a simple machine is a mechanical device that changes the direction or magnitude of a Force. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about It can also be defined as an inclined plane wrapped around a shaft. This article deals with the physical structure For related terms see Canal inclined plane, Cable railway, Funicular, or Fixed-wing

Contents 1 Screws and Bolts 2 Differentiation between bolt and screw 3 Other fastening methods 4 Materials and strength 5 Mechanical analysis 6 Tensile strength 7 Types of screws and bolts 7.1 Fasteners with a tapered shaft (tapping screws) 7.2 Fasteners with a non-tapered shaft 7.3 Other threaded fasteners 8 Shapes of screw head 9 Types of screw drive 9.1 Combination drives 10 Tamper-resistant screws 11 Tools used 12 Mechanics of use 13 Thread standards 13.1 ISO metric screw thread 13.2 Whitworth 13.3 British Association screw threads (BA) 13.4 Unified Thread Standard 13.5 Others 14 History 15 Legal issues 16 See also 17 References 18 External links

Screws and Bolts

A screw used as a threaded fastener consists of a cylindrical shaft, which in many cases tapers to a point at one end, and with a helical ridge or thread formed on it, and a head at the other end which can be rotated by some means. The thread is essentially an inclined plane wrapped around the shaft. The thread mates with a complementary helix in the material. The material may be manufactured with the mating helix using a tap, or the screw may create it when first driven in (a self-tapping screw). Taps and dies are cutting tools used to create Screw threads in solid substances including but not limited to Metal, Wood, and Plastic. Self-tapping is the ability of a Screw to advance when turned while creating its own thread The head is specially shaped to allow a screwdriver or wrench (British English: spanner) to rotate the screw, driving it in or releasing it. The screwdriver is a device specifically designed to insert and tighten or to loosen and remove Screws The screwdriver comprises a head or tip which engages with A wrench or spanner is a Tool used to provide a Mechanical advantage in applying Torque to turn bolts, nuts or British English or UK English ( BrE, BE, en-GB) is the broad term used to distinguish the forms of the English language used in the The head is of larger diameter than the body of the screw and has no thread so that the screw can not be driven deeper than the length of the shaft, and to provide compression.

Screws can normally be removed and reinserted without reducing their effectiveness. They have greater holding power than nails and permit disassembly and reuse. In Engineering, Woodworking and Construction, a nail is a pin -shaped sharp object of hard Metal, typically Steel,

The vast majority of screws are tightened by clockwise rotation; we speak of a right-hand thread. A clockwise motion is one that proceeds 'like the Clock 's hands' from the top to the right then down and then to the left and back to the top Screws with left-hand threads are used in exceptional cases, when the screw is subject to anticlockwise forces that might undo a right-hand thread. Left-hand screws are used on rotating items such as the left-hand grinding wheel on a bench grinder or the left hand pedal on a bicycle (both looking towards the equipment) or hub nuts on the left side of some automobiles. A bench grinder or pedestal grinder is a machine used to drive an abrasive wheel (or wheels A bicycle Pedal is the part of a Bicycle that the rider pushes with his or her foot to propel the bicycle The bicycle, cycle, or bike is a pedal-driven, human-powered vehicle with two wheels attached to a frame, one behind

Threaded fasteners were made by a cutting action such as dies provide, but recent advances in tooling allow them to be made by rolling an unthreaded rod (the blank) between two specially machined dies which squeeze the blank into the shape of the required fastener, including the thread. Taps and dies are cutting tools used to create Screw threads in solid substances including but not limited to Metal, Wood, and Plastic. A die is a specialized Tool used in Manufacturing industries to cut shape and form a wide variety of products and components This method has the advantages of work hardening the thread and saving material. Work hardening, strain hardening, or cold work is the strengthening of a material by macroscopically speaking plastic deformation (which has the A rolled thread can be distinguished from a thread formed by a die as the outside diameter of the thread is greater than the diameter of the unthreaded portion of the shaft. Bicycle spokes, which are just bolts with long thin unthreaded portions, always use rolled threads for strength.

Differentiation between bolt and screw

A universally accepted distinction between a screw and a bolt does not exist.

In common usage the term screw refers to smaller (less than 1/4 inch) threaded fasteners, especially threaded fasteners with tapered shafts and the term bolt refers to larger threaded fasteners that do not have tapered shafts. The term machine screw is commonly used to refer to smaller threaded fasteners that do not have a tapered shaft.

Various methods of distinguishing bolts and screws exist or have existed. These methods conflict at times and can be confusing. Old SAE and USS standards made a distinction between a bolt and a cap screw based on whether a portion of the shaft was un-threaded or not. Cap screws had shafts that were threaded up to the head and bolts had partially threaded shafts. Today a bolt that has a completely threaded shaft might be referred to as a tap bolt.

ASME B18. 2. 1 defines a bolt as "an externally threaded fastener designed for insertion through the holes in assembled parts, and is normally intended to be tightened or released by torquing a nut". Using this definition to determine whether a particular threaded fastener is a screw or a bolt requires that an assumption be made about the intended purpose of the threaded fastener and as a practical matter doesn't seem to be followed by most threaded fastener manufacturers. It also conflicts with common usage such as the term, "head bolt", which is a threaded fastener that mates with a tapped hole in an engine block and is not intended to mate with a nut.

It is possible to find other distinctions than those described above, but regardless of the particular distinction favored by an individual or standards body the use of the term screw or bolt varies. More specific terms for threaded fastener types that include the word screw or bolt (such as machine screw or carriage bolt) have more consistent usage and are the common way to specify a particular kind of fastener.

The US government made an effort to formalize the difference between a bolt and a screw because different tariffs apply to each. The document seems to have no significant effect on common usage and does not eliminate the ambiguous nature of the distinction for some fasteners. It is available here.

Other fastening methods

Alternative fasteners to screws and bolts are nails, rivets, roll pins, pinned shafts, welding, soldering, brazing, gluing (including taping). A rivet is a mechanical Fastener. Before it is installed it consists of a smooth cylindrical shaft with a head on one end Clinker building is a method of constructing hulls of Boats and Ships by fixing Wooden planks and in the early nineteenth century Welding is a fabrication process that joins materials usually Metals or Thermoplastics by causing coalescence. A solder is a fusible metal Alloy with a melting point or melting range of 90 to 450 ° C (200 to 840 ° F) used in a process called Brazing is a joining process whereby a Filler metal or Alloy is heated to melting temperature above - or by the traditional definition in the United States Polyvinyl acetate ( PVA or PVAc) is a Rubbery Synthetic polymer.

Another option is the threaded insert. Thread repair inserts are fastener elements used for one of two purposes To repair a Stripped threaded hole Examples include Helical Inserts [1] and Keensert [2].

Materials and strength

Screws and bolts are made in a wide range of materials, with steel being perhaps the most common, in many varieties. Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 Where great resistance to weather or corrosion is required, stainless steel, titanium, brass, bronze, monel or silicon bronze may be used, or a coating such as brass, zinc or chromium applied. Titanium (taɪˈteɪniəm is a Chemical element with the symbol Ti and Atomic number 22 Brass is any Alloy of Copper and Zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties Bronze is any of a broad range of Copper alloys, usually with Tin as the main additive but sometimes with other elements such as Phosphorus Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 Electrolytic action from dissimilar metals can be prevented with aluminium screws for double-glazing tracks, for example. WikipediaNaming Some types of plastic, such as nylon or Teflon, can be threaded and used for fastening requiring moderate strength and great resistance to corrosion or for the purpose of electrical insulation. Overview Nylon is a Thermoplastic silky material first used commercially in a nylon- Bristled Toothbrush (1938 followed more famously by In Chemistry, poly(tetrafluoroethene or poly(tetrafluoroethylene ( PTFE) is a synthetic Fluoropolymer which finds numerous applications An insulator, also called a Dielectric, is a material that resists the flow of Electric current. Even porcelain and glass can have molded screw threads that are used successfully in applications such as electrical line insulators and canning jars. Mass-produced glass canning jars, also known as Mason jars after their inventor John L

The same type of screw or bolt can be made in many different grades of material. For critical high-tensile-strength applications, low-grade bolts may fail, resulting in damage or injury. On SAE-standard bolts, a distinctive pattern of marking is impressed on the heads to allow inspection and validation of the strength of the bolt. However, low-cost counterfeit fasteners may be found with actual strength far less than indicated by the markings. A counterfeit is an imitation that is made usually with the intent to deceptively represent its content or origins Such inferior fasteners are a danger to life and property when used in aircraft, automobiles, heavy trucks, and similar critical applications.

In some applications joints are designed so that the screw or bolt will intentionally fail before more expensive components. In this case replacing an existing fastener with a higher strength fastener can result in equipment damage. Thus it is generally good practice to replace fasteners with the same grade originally installed.

Mechanical analysis

A screw or bolt is a specialized application of the inclined plane. The inclined plane, called its thread, is helically disposed around a cylinder or shaft. That thread usually either fits into a corresponding (negative or female) helical thread in a nut, or forms a corresponding helical cut in surrounding softer material as it is inserted. A simple screw, such as for fastening, is typically pointed, and thereby is commonly distinguished (in informal terminology) from a bolt or machine screw. Common screws, and usually bolts, have a head which may be mechanically driven or rotated, which usually serves as a stop, and may have an unthreaded shoulder portion beneath the head.

The technical analysis (see also statics, dynamics) to determine the pitch, thread profile, coefficient of friction (static and dynamic), and holding power of a screw or bolt is very similar to that performed to predict wedge behavior. Statics is the branch of Mechanics concerned with the analysis of loads ( Force, torque/moment) on Physical systems in Static equilibrium In physics the term dynamics customarily refers to the time evolution of physical processes Wedges are discussed in the article on simple machines. In Physics, especially Mechanics, a simple machine is a mechanical device that changes the direction or magnitude of a Force.

Critical applications of screws and bolts will specify a torque that must be applied when driving it. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about The main concept is to tension the bolt, and compress parts being held together, creating a spring-like assembly. A spring is a flexible elastic object used to store mechanical Energy. The stress thus introduced to the bolt is called a preload. When external forces try to separate the parts, the bolt experiences no strain unless the preload force is exceeded.

As long as the preload is never exceeded, the bolt or nut will never come loose (assuming the full strength of the bolt is used. If the full strength of the bolt is not used (for example, a steel bolt threaded into aluminium, then a thread-locking adhesive or insert may be used. WikipediaNaming

If the preload is exceeded during normal use, the joint will eventually fail. The preload is calculated as a percentage of the bolt's yield tensile strength, or the strength of the threads it goes into, or the compressive strength of the clamped layers (plates, washers, gaskets), whichever is least. The yield strength or yield point of a Material is defined in Engineering and Materials science as the stress at which a material Tensile strength \sigma_{UTS} or S_U is the Stress at which a material breaks or permanently deforms A washer is a thin plate (typically disk-shaped with a hole (typically in the middle that is normally used to distribute the load of a threaded fastener. A gasket is a mechanical seal that fills the space between two objects generally to prevent leakage between the two objects while under compression.

Tensile strength

Screws and bolts are usually in tension when properly fitted. In most applications they are not designed to bear large shear forces. In Physics, a force is whatever can cause an object with Mass to Accelerate. For example, when two overlapping metal bars joined by a bolt are likely to be pulled apart longitudinally, the bolt must be tight enough so that the friction between the two bars can overcome the longitudinal force. Theory The clamp load also called preload of a cap screw is created when a torque is applied and is generally a percentage of the cap screw's proof strength Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e If the bars slip, then the bolt may be sheared in half, or friction between the bolt and slipping bars may erode and weaken the bolt (called fretting). For this type of application, high-strength steel bolts are used and should be tightened to a specified torque. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about

High-strength steel bolts usually have a hexagonal head with an ISO strength rating (called property class) stamped on the head. The property classes most often used are 5. 8, 8. 8, and 10. 9. The number before the point is the tensile ultimate strength in MPa divided by 100. Tensile strength \sigma_{UTS} or S_U is the Stress at which a material breaks or permanently deforms The number after the point is 10 times the ratio of tensile yield strength to tensile ultimate strength. For example, a property class 5. 8 bolt has a nominal (minimum) tensile ultimate strength of 500 MPa, and a tensile yield strength of 0. 8 times tensile ultimate strength or 0. 8(500) = 400 MPa.

Tensile ultimate strength is the stress at which the bolt fails (breaks in half). Tensile yield strength is the stress at which the bolt will receive a permanent set (an elongation from which it will not recover when the force is removed) of 0. 2 % offset strain. The yield strength or yield point of a Material is defined in Engineering and Materials science as the stress at which a material When elongating a fastener prior to reaching the yield point, the fastener is said to be operating in the elastic region; whereas elongation beyond the yield point is referred to as operating in the plastic region, since the fastener has suffered permanent plastic deformation.

Mild steel bolts have property class 4. 6. High-strength steel bolts have property class 8. 8 or above. An M10, property class 8. 8 bolt can very safely hold a static tensile load of about 15 kN. The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical

There is no method to measure the tension of a bolt already in place other than to tighten it and identify at which point the bolt starts moving. This is known as 're-torqueing'. An electronic torque wrench is used on the bolt under test, and the torque applied is constantly measured. When the bolt starts moving (tightening) the torque briefly drops sharply - this drop-off point is considered the measure of tension.

Types of screws and bolts

Threaded fasteners either have a tapered shaft or a non-tapered shaft. Fasteners with tapered shafts are designed to either be driven into a substrate directly or into a pilot hole in a substrate. Mating threads are formed in the substrate as these fasteners are driven in. Fasteners with a non-tapered shaft are designed to mate with a nut or to be driven into a tapped hole.

Fasteners with a tapered shaft (tapping screws)

• Screw - There is not a universally accepted definition of the word, screw. A drill (from Dutch Drillen) is It generally refers to a smaller threaded fastener with a tapered shaft. See the Differentiation Between Bolt and Screw section above for a more detailed discussion.
• Wood Screw – Generally has an un-threaded portion of the shaft below the head. It is designed to attach two pieces of wood together.
• Lag Screw (Lag Bolt) – Similar to a wood screw except that it is generally much larger running to lengths up to 15 inches (381 mm) with diameters from a quarter inch to 1/2 inches (6. Inches redirects here To see the Les Savy Fav album see Inches. The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to 4 mm-12. 25 mm) in commonly available (hardware store) sizes (not counting larger mining and civil engineering lags and lag bolts) and it generally has a hexagonal head drive head. Lag bolts are design for securely fastening heavy timbers (post and beams, timber railway trestles and bridges) to one another, or to fasten wood to masonry or concrete. Timber framing (Fachwerk or Half-timbering, is the method of creating framed structures of heavy timber jointed together with pegged Mortise and tenon joints
  • Lag bolts are usually used with an expanding insert called a lag in masonry or concrete walls, the lag manufactured with a hard metal jacket that bites into the sides of the drilled hole, and the inner metal in the lag being a softer alloy of lead, or zinc amalgamated with soft iron. The coarse thread of a lag bolt and lag mesh and deform slightly making a secure near water tight anti-corroding mechanically strong fastening.
• Sheet Metal Screw (Self-tapping Screw, thread cutting screws) - Has sharp threads that cut into a material such as sheet metal, plastic or wood. They are sometimes notched at the tip to aid in chip removal during thread cutting. The shaft is usually threaded up to the head. Sheet metal screws make excellent fasteners for attaching metal hardware to wood because the fully thread shaft provides good retention in wood.
• Self-drilling screw (Teks^(R) screw) - Similar to a sheet metal screw, but it has a drill-shaped point to cut through the substrate to eliminate the need for drilling a pilot hole. Designed for use in soft steel or other metals.
• Drywall screw - Specialized screw with a bugle head that is designed to attach drywall to wood or metal studs, however it is a versatile construction fastener with many uses. The diameter of drywall screw threads is larger than the shaft diameter.
• Particle Board Screw (Chipboard Screw) - Similar to a drywall screw except that it has a thinner shaft and provides better holding power in particle board.
• Deck Screw - Similar to drywall screw except that it is has improved corrosion resistance and is generally supplied in a larger gauge.
• Double ended screw (Dowel screw) - Similar to a wood screw but with two pointed ends and no head, used for making hidden joints between two pieces of wood.
• Screw Eye(Eye Screw) - Screw with a looped head. Larger ones are sometimes call lag eye screws. Designed to be used as attachment point, particularly for something that is hung from it.

Fasteners with a non-tapered shaft

• Bolt - There is not a universally accepted definition of the word bolt. It generally refers to a larger threaded fastener with a non-tapered shaft. See the Differentiation Between Bolt and Screw section above for a more detailed discussion.
• Cap Screw – In places the term is used interchangeably with bolt. In the past the term, cap screw was restricted to threaded fasteners with a shaft that is threaded all the way to the head, however this is now a non-standard usage.
• Hex Cap Screw – Cap screw with a hexagonal head, designed to be driven by a wrench (spanner). An ASME B18. 2. 1 compliant cap screw has somewhat tighter tolerances than a hex bolt for the head height and the shaft length. The nature of the tolerance difference allows an ASME B18. 2. 1 hex cap screw to always fit where a hex bolt is installed but a hex bolt could be slightly too large to be used where a hex cap screw is designed in.
• Hex Bolt - At times the term is used interchangeably with hex cap screw. An ASME B18. 2. 1 compliant hex bolt is built to different tolerances than a hex cap screw.
• Socket Cap Screw – Cap screw with a hexagonal recessed drive (Allen), usually with a cylindrical head, but can also be found with a rounded button head or a countersunk flat head.
• Machine screw - Generally a smaller fastener (less than 1/4 inch in diameter) threaded the entire length of its shaft that usually has a recessed drive type (slotted, Phillips, etc. ).
• Self Tapping Machine Screw – Similar to a machine screw except the lower part of the shaft is designed to cut threads as the screw is driven into an un-tapped hole. The advantage of this s crew over a self tapping screw is that if the screw is reinstalled new threads are not cut as the screw is driven.
• Set screw (grub screw) - Generally a headless screw but can be any screw used to fix a rotating part to a shaft. The set screw is driven through a threaded hole in the rotating part until it is tight against the shaft.
• Tap Bolt - A bolt that is threaded all the way to the head. An ASME B18. 2. 1 compliant tap bolt has the same tolerances as an ASME B18. 2. 1 compliant hex cap screw.
• Stud - similar to a bolt but without the head. Studs are threaded on both ends. In some cases the entire length of the stud is threaded, while in other cases there will be an un-threaded section in the middle. (See also: screw anchor, wedge anchor. A screw anchor is a Fastener that can attach one object to another in situations where screws nails adhesives or other simple fasteners are either impractical or ineffective A wedge anchor is a type of Fastener used to attach a fixture to a solid base material (such as Concrete) )
• Eye Bolt – A bolt with a looped head.
• Toggle Bolt – A bolt with a special nut known as a wing. It is designed to be used where there is no access to side of the material where the nut is located. Usually the wing is spring loaded and expands after being inserted into the hole.
• Carriage Bolt (Coach Bolt) - Has a domed or countersunk head, and the shaft is topped by a short square section under the head. The square section grips into the part being fixed (typically wood), preventing the bolt from turning when the nut is tightened. A rib neck carriage bolt has several longitudinal ribs instead of the square section, to grip into a metal part being fixed.
• Stove Bolt - Similar to a carriage bolt, but usually used in metal. It requires a square hole in the metal being bolted to prevent the bolt from turning.
• Shoulder Screw - Screw used for revolving joints in mechanisms and linkages. The shaft of the screw is smooth and works as a bearing surface. There is a reduced diameter thread at the end of the cylindrical bearing surface.
• Thumb Screw – A threaded fastener designed to be twisted into a tapped hole by hand without the use of tools.
• Tension Control Bolt (TC Bolt) – Heavy duty bolt used in steel frame construction. The head is usually domed and is not designed to be driven. The end of the shaft has a spline on it which is engaged by a special power wrench which prevents the bolt from turning while the nut is tightened. When the appropriate torque is reached the spline shears off.

Other threaded fasteners

• Thread rolling screws - have a lobed (usually triangular) cross section. They form threads by pushing outward during installation. They may have tapping threads or machine threads.
• Superbolt, or Multi-Jackbolt Tensioner Alternative type of fastener that retrofits or replaces existing nuts, bolts, or studs. Tension in the bolt is developed by torquing individual jackbolts which are threaded through the body of the nut and push against a hardened washer. Installation and removal of any size tensioner is achieved with hand tools, which can be advantageous when dealing with large diameter bolting applications.
• Hanger Screw – A headless fastener that has machine screw threads on one end and self tapping threads on the other designed to be driven into wood or another soft substrate. Often used for mounting legs on tables.

Teks^(R) is a registered trademark of ITW Buildex

Shapes of screw head

• pan head: a low disc with chamfered outer edge. In Clothing and Fashion design, a button is a small plastic or metal disc- or knob-shaped typically round object usually attached to an article of Clothing In Architecture and Structural engineering, a truss is a structure comprising one or more triangular units constructed with straight slender members whose A countersink is a conical hole cut into a manufactured object or the cutter used to cut such a hole In geometry an oval or ovoid (from Latin ovum, 'egg' is any Curve resembling an egg or an Ellipse. A chamfer is a Beveled edge connecting two surfaces If the surfaces are at right angles the chamfer will typically be symmetrical at 45 degrees
• button or dome head: cylindrical with a rounded top.
• round head: dome-shaped, commonly used for machine screws.
• truss head: lower-profile dome designed to prevent tampering.
• flat head or countersunk: conical, with flat outer face and tapering inner face allowing it to sink into the material.
• oval or raised head: countersunk with a rounded top.
• bugle head: similar to countersunk, but there is a smooth progression from the shaft to the angle of the head, similar to the bell of a bugle. "Bugler" redirects here For the tobacco brand see Bugler (tobacco.
• cheese head: disc with cylindrical outer edge, height approximately half the head diameter.
• fillister head: cylindrical, but with a slightly convex top surface.
• socket head: cylindrical, relatively high, with different types of sockets (hex, square, torx, etc. Star key redirects here For the key on a telephone keyboard see Asterisk. ).
• mirror screw head: countersunk head with a tapped hole to receive a separate screw-in chrome-plated cover, used for attaching mirrors.
• headless (set or grub screw): has either a socket or slot in one end for driving.

Some varieties of screw are manufactured with a break-away head, which snaps off when adequate torque is applied. This prevents tampering and disassembly and also provides an easily-inspectable joint to guarantee proper assembly.

Types of screw drive

Part of the series on
Screw drive types
	Slotted
	Phillips ("Crosshead")
	Pozidriv (SupaDriv)
	Torx
	Hex (Allen)
	Robertson
	Tri-Wing
	Torq-Set
	Spanner Head
	Triple Square (XZN)
Others:
polydrive, spline drive, double hex
This box: view • talk • edit

Modern screws employ a wide variety of drive designs, each requiring a different kind of tool to drive in or extract them. The most common screw drives are the slotted and Phillips; hex, Robertson, and TORX are also common in some applications. Some types of drive are intended for automatic assembly in mass-production of such items as automobiles. More exotic screw drive types may be used in situations where tampering is undesirable, such as in electronic appliances that should not be serviced by the home repair person.

• Slot head has a single slot, and is driven by a flat-bladed screwdriver. The slotted screw is common in woodworking applications, but is not often seen in applications where a power driver would be used, due to the tendency of a power driver to slip out of the head and potentially damage the surrounding material.
• Cross-head, cross-point, or cruciform has a "+"-shaped slot and is driven by a cross-head screwdriver, designed originally for use with mechanical screwing machines. There are five types:
  • The Phillips screw drive has slightly rounded corners in the tool recess, and was designed so the driver will slip out, or cam out, under high torque to prevent over-tightening. To cam out (or cam-out is a process by which a Screwdriver slips out of the head of a Screw being driven once the Torque required to turn the screw The Phillips Screw Company was founded in Oregon in 1933 by Henry F. Phillips, who bought the design from J. Henry F Phillips (1890 &ndash 1958 a US businessman from Portland Oregon, has the honor of having the Phillips-head Screw and Screwdriver P. Thompson. Phillips was unable to manufacture the design, so he passed the patent to the American Screw Company, who was the first to manufacture it.
  • A Reed & Prince or Frearson screw drive is similar to a Phillips but has a more pointed 75° V shape. Its advantage over the Phillips drive is that one driver or bit fits all screw sizes. It is found mainly in marine hardware and requires a special screw driver or bit to work properly. The tool recess is a perfect cross, unlike the Phillips head, which is designed to cam out. It was developed by an English inventor named Frearson in the 19th century and produced from the late 1930s to the mid-1970s by the former Reed & Prince Manufacturing Company of Worcester, Massachusetts, a company which traces its origins to Kingston, Massachusetts, in 1882, and was liquidated in 1990 with the sale of company assets. Worcester (ˈwʊstɚ is a City in the state of Massachusetts in the United States of America. The company is now in business.
  • A JIS (Japanese Industrial Standard) head, commonly found in Japanese equipment, looks like a Phillips screw, but is designed not to cam out and will, therefore, be damaged by a Phillips screwdriver if it is too tight. This article is about Japanese Industrial Standards in general see JIS encoding for the character encoding used in representing the Japanese language for computer software Heads are usually identifiable by a single dot to one side of the cross slot. The standard number is JIS B 1012:1985
  • French Recess, also called BNAE NFL22-070 for Bureau de Normalisation de l'Aéronautique et de l'Espace, a French standards organization. A standards organization, standards body, standards development organization or SDO is any entity whose primary activities are developing coordinating
  • Pozidriv is patented, similar to cross-head but designed not to slip, or cam out. The Pozidriv (or SupaDriv) is a type of Screw head and Screwdriver, jointly patented by the Phillips Screw Company and American Screw Company It has four additional points of contact, and does not have the rounded corners that the Phillips screw drive has. Phillips screwdrivers will usually work in Pozidriv screws, but Pozidriv screwdrivers are likely to slip or tear out the screw head when used in Phillips screws. Heads are marked with single lines at 45 degrees to the cross recess, for identification. (note that two lines at 45 are a different recess: a very specialised Phillips screw). Pozidriv was jointly patented by the Phillips Screw Company and American Screw Company in the USA. Developed by GKN in the 1960s, the recess is licenced from Trifast PLC in the rest of the world. GKN plc ( is a leading British Engineering company The Company was formerly known as Guest Keen and Nettlefolds and can tracing its origins back
  • Supadriv is similar to Pozidriv. The Pozidriv (or SupaDriv) is a type of Screw head and Screwdriver, jointly patented by the Phillips Screw Company and American Screw Company
• TORX is a star-shaped "hexalobular" drive with six rounded points. Star key redirects here For the key on a telephone keyboard see Asterisk. It was designed to permit increased torque transfer from the driver to the bit compared to other drive systems. TORX is very popular in the automotive and electronics industries due to resistance to cam out and extended bit life, as well as reduced operator fatigue by minimizing the need to bear down on the drive tool to prevent cam out. TORX screws were found in early Apple Macintosh computers, to discourage home repairs. Macintosh, commonly nicknamed Mac is a Brand name which covers several lines of Personal computers designed developed and marketed by Apple Inc TORX PLUS is an improved version of TORX which extends tool life even further and permits greater torque transfer compared to TORX. A tamper-resistant TORX head has a small pin inside the recess. The tamper-resistant TORX is also made in a 5 lobed variant. These "5-star" TORX configurations are commonly used in correctional facilities, public facilities and government schools, but can also be found in some electronic devices, such as Seagate's external drives. Seagate ( is the world's largest manufacturer of hard drives and storage solutions
• TTAP is an improved "hexalobular" drive for without wobbling and stable stick-fit. Star key redirects here For the key on a telephone keyboard see Asterisk. TTAP is backward convertible with generic hexalobular drive.

• Hexagonal (hex) socket head has a hexagonal hole and is driven by a Hex Wrench, sometimes called an Allen key or Hex key, or by a power tool with a hexagonal bit. A hex key, also known as an Allen, Alum, hex-head, or zeta key or wrench is a Tool used to drive Screws and bolts Tamper-resistant versions with a pin in the recess are available. Hex sockets are increasingly used for modern bicycle parts because hex wrenches are very light and easily carried tools. They are also frequently used for self-assembled furniture (e. g. from Ikea). IKEA is a privately-held international home products retailer that sells flat pack Furniture, accessories bathrooms and kitchens at retail stores around the world
• Robertson head, invented in 1908 by P. A Robertson screwdriver (also called a square drive screwdriver is a type of Screwdriver with a square -shaped tip with a slight taper (in the same way that flatheads L. Robertson, has a square hole and is driven by a special power-tool bit or screwdriver. The screw is designed to maximize torque transferred from the driver, and will not slip, or cam out. It is possible to hold a Robertson screw on a driver bit horizontally or even pendant, due to a slight wedge fit. Commonly found in Canada in carpentry and woodworking applications and in Canadian-manufactured electrical wiring items such as receptacles and switch boxes. Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page
• Square-drive head is an American clone of the Robertson that has a square hole without taper. Due to the lack of taper, the hole must be oversize relative to the screwdriver, and is much more likely to strip than the Robertson.
• Tri-Wing head has a triangular slotted configuration. The Tri-Wing is a type of screw and screw head It is sometimes called a triangular slotted screw. They were used by Nintendo on several consoles and accessories, including the Game Boy, Wii, and Wii Remote, and on some Nokia phones and chargers to discourage home repair. is a Multinational corporation headquartered in Kyoto Japan founded on The is a handheld video game console developed and manufactured by Nintendo. The Wii Remote, sometimes Nicknamed " Wiimote " is the primary controller for Nintendo 's Nokia Corporation (pronunciation /'nɔkiɑ/),,) is a Finnish multinational Communications Corporation, headquartered
• Torq-Set or offset cruciform may be confused with Phillips; however, the four legs of the contact area are offset in this drive type. Is commonly used in the aerospace industry.
• Spanner drive uses two round holes opposite each other, and is designed to prevent tampering. Commonly seen in elevators in the United States. An elevator or lift is a Transport device used to move people or goods vertically from one floor to another The United States of America —commonly referred to as the
• Clutch Type A or standard clutch head resembles a bow tie. The bow tie is a men's Necktie popularly worn with Formal attire, such as suits or Dinner jackets It consists of a ribbon of fabric tied around These were common in GM automobiles, trucks and buses of the 1940s and 1950s, particularly for body panels. General Motors Corporation ( GM) ( is a multinational automobile manufacturer founded in 1908 and headquartered in the United States.
• Clutch Type G head resembles a butterfly. This type of screw head is commonly used in the manufacture of mobile homes and recreational vehicles. Mobile homes or static caravans are prefabricated homes built in factories rather than on site and then taken to the place where they will be occupied In North American English the term recreational vehicle, and its acronym RV, are generally used to refer to an enclosed piece of equipment dually used as both

Combination drives

Some screws have heads designed to accommodate more than one kind of driver, sometimes referred to as combo-head or combi-head. The most common of these is a combination of a slotted and Phillips head, often used in attaching knobs to furniture drawer fronts. Because of its prevalence, there are now drivers made specifically for this kind of screw head. Other combinations are a Phillips and Robertson, a Robertson and a slotted, a Torx and a slotted, and a triple-drive screw which can take a slotted, Phillips or a Robertson. The Recex drive system claims it offers the combined non-slip convenience of a Robertson drive during production assembly and Phillips for after market serviceability. Quadrex is another Phillips/Robertson drive. Phillips Screw Company offers both Phillips and Pozidriv(sic) combo heads with Robertson.

Tamper-resistant screws

Many screw drives, including Phillips, TORX, and Hexagonal, are also manufactured in tamper-resistant form. These typically have a pin protruding in the center of the screw head, necessitating a special tool for extraction. In some variants the pin is placed slightly off-center, requiring a correspondingly shaped bit. However, the bits for many tamper-resistant screw heads are now readily available from hardware stores, tool suppliers and through the Internet. What is more, there are many commonly used techniques to extract tamper resistant screws without the correct driver — for example, the use of an alternative driver that can achieve enough grip to turn the screw, modifying the head to accept an alternative driver, forming ones own driver by melting an object into the head to mould a driver, or simply turning the screw using a pair of locking pliers. Pliers are Hand tools designed primarily for gripping objects by using Leverage. Thus, these special screws offer only modest security.

The slotted screw drive also comes in a tamper-resistant one-way design with sloped edges; the screw can be driven in, but the bit slips out in the reverse direction.

There are specialty fastener companies that make unusual, proprietary head designs, featuring matching drivers available only from them, and only supplied to registered owners^[1]. An example of this would be the attachment for the wheels and/or spare tires of some types of car; one of the nuts may require a specialized socket (provided with the car) to prevent theft.

The break away bolt is a high security fastener that is extremely difficult to remove. It consists of a counter-sunk flat head screw, with a thin shaft and hex head protruding from the flat head. The hex head is used to drive the bolt into the countersunk hole, then the wrench or hammer is used to knock the shaft and hex head off of the flat head, leaving only a smooth screw head exposed. Removal is facilitated by drilling a small hole part way into the outer part of the head and using a punch and hammer at a sharp angle in a counter-clockwise direction. A hammer is a tool meant to deliver an impact to an object The most common uses are for driving nails fitting parts and breaking up objects This type of screw is used primarily in prison door locks.

Tools used

The hand tool used to drive in most screws is called a screwdriver. A power tool that does the same job is a power screwdriver; power drills may also be used with screw-driving attachments. A drill (from Dutch Drillen) is Where the holding power of the screwed joint is critical, torque-measuring and torque-limiting screwdrivers are used to ensure sufficient but not excessive force is developed by the screw. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about The hand tool for driving cap screws and other types is called a spanner (UK usage) or wrench (US usage). A wrench or spanner is a Tool used to provide a Mechanical advantage in applying Torque to turn bolts, nuts or

Mechanics of use

When driving in a screw, especially when the screw has been removed and is being placed again, the threads can become misaligned and damage, or strip, the threading of the hole. To avoid this, slight pressure is applied and the screw is driven in reverse, until the leading edges of the helices pass each other, at which point a slight click will be felt (and sometimes heard. ) When this happens, the screw will often assume a more aligned position with respect to the hole.

Immediately after the 'click', the screw may be driven in without damage to the threading. This technique is useful for re-seating screws in wood and plastic, and for assuring the proper fit when screwing down plates and covers where alignment is difficult.

Thread standards

See also: Screw thread

There are many systems for specifying the dimensions of screws, but in much of the world the ISO metric screw thread preferred series has displaced the many older systems. A screw thread is a helical or tapered structure used to convert between rotational and linear movement or force The ISO metric screw threads are the world-wide most commonly used type of general-purpose Screw thread. Other relatively common systems include the British Standard Whitworth, BA system (British Association), and the SAE Unified Thread Standard. British Association or BA screw threads are a largely obsolete set of small Screw threads the largest being 0BA at 6 mm diameter SAE International (SAE is a professional organization for mobility engineering professionals in the Aerospace, Automotive, and commercial Vehicle industries The Unified Thread Standard ( UTS) defines a standard thread form and series—along with allowances tolerances and designations—for Screw threads commonly

ISO metric screw thread

The basic principles of the ISO metric screw thread are defined in international standard ISO 68-1 and preferred combinations of diameter and pitch are listed in ISO 261. International standards are Standards developed by international Standards organisations International standards are available for consideration and use worldwide The ISO metric screw threads are the world-wide most commonly used type of general-purpose Screw thread. The smaller subset of diameter and pitch combinations commonly used in screws, nuts and bolts is given in ISO 262. The ISO metric screw threads are the world-wide most commonly used type of general-purpose Screw thread. The most commonly used pitch value for each diameter is known as the "coarse pitch". For some diameters, one or two additional "fine pitch" variants are also specified, for special applications such as threads in thin-walled pipes. ISO metric screw threads are designated by the letter M followed by the major diameter of the thread in millimeters, e. g. "M8". If the thread does not use the normal "coarse pitch" (e. g. , 1. 25 mm in the case of M8), then the pitch in millimeters is also appended with a multiplication sign, e. The multiplication sign is the symbol × ( multiplication sign is the preferred Unicode name for the Codepoint represented by that Glyph g. "M8×1" if the screw thread has an outer diameter of 8 mm and advances by 1 mm per 360° rotation.

The nominal diameter of a metric screw is the outer diameter of the thread. The tapped hole (or nut) into which the screw fits, has an internal diameter which is the size of the screw minus the pitch of the thread. Thus, an M6 screw, which has a pitch of 1 mm, is made by threading a 6 mm shaft, and the nut or threaded hole is made by tapping threads in a 5 mm hole.

Metric hexagon bolts, screws and nuts are specified, for example, in British Standard BS 4190 (general purpose screws) and BS 3692 (precision screws). Regular hexagon The internal Angles of a regular hexagon (one where all sides and all angles are equal are all 120 ° and the hexagon has 720 degrees British Standards are produced by BSI British Standards, a division of BSI Group that is incorporated under a Royal Charter and is formally designated The following table lists the relationship given in these standards between the thread size and the maximal width across the hexagonal flats (wrench size):

ISO metric thread	M1. 6	M2	M2. 5	M3	M4	M5	M6	M8	M10	M12	M16	M20	M24	M30	M36	M42	M48	M56	M64
wrench size (mm)	3. 2	4	5	5. 5	7	8	10	13	17	19	24	30	36	46	55	65	75	85	95

In addition, the following non-preferred intermediate sizes are specified:

ISO metric thread	M14	M18	M22	M27	M33	M39	M45	M52	M60	M68
wrench size (mm)	22	27	32	41	50	60	70	80	90	100

Whitworth

The first person to create a standard (in about 1841) was the English engineer Sir Joseph Whitworth. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland An engineer is a person professionally engaged in a field of Engineering. Sir Joseph Whitworth Baronet ( December 21, 1803 &ndash January 22, 1887) was an English Engineer and Entrepreneur Whitworth screw sizes are still used, both for repairing old machinery and where a coarser thread than the metric fastener thread is required. Whitworth became British Standard Whitworth, abbreviated to BSW (BS 84:1956) and the British Standard Fine (BSF) thread was introduced in 1908 because the Whitworth thread was a bit coarse for some applications. The thread angle was 55° and a depth and pitch of thread that varied with the diameter of the thread (i. e. , the bigger the bolt, the coarser the thread). The spanner size is determined by the size of the bolt, not the distance between the flats.

The most common use of a Whitworth pitch nowadays is the standard photographic tripod thread, which for small cameras is 1/4" Whitworth (20 tpi) and for medium/large format cameras is 3/8" Whitworth (16 tpi). In Photography, a tripod is a three-legged stand for a Camera, used to stabilize and elevate the camera It is also used for microphone stands and their appropriate clips, again in both sizes, along with "thread adapters" to allow the smaller size to attach to items requiring the larger thread.

British Association screw threads (BA)

A later standard established in the United Kingdom was the BA system, named after the British Association for Advancement of Science. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located British Association or BA screw threads are a largely obsolete set of small Screw threads the largest being 0BA at 6 mm diameter Screws were described as "2BA", "4BA" etc. , the odd numbers being rarely used, except in equipment made prior to the 1970's for telephone exchanges in the UK. This equipment made extensive use of odd-numbered BA screws, in order -- it may be suspected -- to reduce theft. While not related to ISO metric screws, the sizes were actually defined in metric terms, a 0BA thread having a 1 mm pitch. These are still the most common threads in some niche applications. Certain types of fine machinery, such as moving-coil meters, tend to have BA threads wherever they are manufactured.

Unified Thread Standard

The United States of America has its own system, usually called the Unified Thread Standard, which is also extensively used in Canada and in most other countries around the world. The Unified Thread Standard ( UTS) defines a standard thread form and series—along with allowances tolerances and designations—for Screw threads commonly Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page At least 85% of the world's fasteners are dimensioned to Unified thread dimensions, and the biggest selection of fastener sizes and materials are found supplied in this standard. ^[2] A version of this standard, called SAE for the Society of Automotive Engineers, was used in the American automobile industry. SAE International (SAE is a professional organization for mobility engineering professionals in the Aerospace, Automotive, and commercial Vehicle industries The SAE is still associated with inch-based fasteners by the public, even though the U. Inches redirects here To see the Les Savy Fav album see Inches. S. auto industry (and other heavy industries relying on SAE) have gradually converted to ISO preferred series fasteners for some assemblies from the 1970s onward, because global parts sourcing and product marketing favor international standardization. However, all automobiles sold throughout the world contain both metric (engine assemblies) and Imperial fasteners (for example, lug nuts, oxygen sensors, internal electrical assemblies, body fasteners, lamps, steering, brake and suspension parts).

Machine screws are described as 0-80, 2-56, 3-48, 4-40, 5-40, 6-32, 8-32, 10-32, 10-24, etc. up to size 16. The first number can be translated to a diameter using a formula, the second is the number of threads per inch. There is a coarse thread and a fine thread for each size, the fine thread being preferred in thin materials or when slightly greater strength is desired.

The numbering system follows a roughly logarithmic series where an increase in each screw number size approximately doubles the tensile strength of the screw and the screw number is found by , where "d" is the nominal diameter. Using this formula a #5 screw has a major diameter of . 125" (1/8"), a #10 screw has a diameter of . 190" (or 3/16" in practical terms), etc. The formula applies for screw thread numbers #0 and higher, but does NOT apply to smaller Unified miniature screw thread series. Typically screws smaller than size #0 are supplied in the Unified Miniature Series. The formula for number sizes smaller than size #0 is given by , with the zero size being the number of zeros after the first. So a #00 screw is . 047" dia, #000 is . 034" dia, etc.

The number series of machine screws once included odd numbers (7, 9, etc. ) and extended up to #16 or more. Standardization efforts in the late 19th and the early part of the 20th century reduced the range of sizes considerably. Now, it is less common to see machine screws larger than #14, or odd number sizes other than #1, #3 and #5. Even though #14 and #16 screws are still available, they are not as common as sizes #0 through #12.

Sizes 1/4" diameter and larger are designated as 1/4"-20, 1/4"-28, etc. the first number giving the diameter in inches and the second number being threads per inch. Most thread sizes are available in UNC or UC (Unified Coarse Thread, example 1/4"-20) or UNF or UF (Unified Fine Thread, example 1/4"-28).

Others

Other thread systems include Acme thread form, BSP (British standard pipe thread which exists in a taper and non taper variant; used for other purposes as well) and BSC (British Standard Cycle) a 26tpi thread form, CEI (Cycle Engineers Institute, used on bicycles in Britain and possibly elsewhere), British Standard Brass a fixed pitch 26tpi thread, NPT (National Pipe Thread) and NPTF (National Pipe Thread Fuel), and PG (German: "Panzer-Gewinde"), used in thin plate metal, such as for switches and nipples in electrical equipment housings. Acme threads are a common Screw thread profile which offers high strength with ease of machining and assembly The British Standard Pipe thread ( BSP thread is a family of standard Screw thread types that has been adopted internationally for interconnecting and sealing pipe National Pipe Thread Tapered ( NPT) is a US standard for tapered threads used to join pipes and fittings

History

In antiquity, the screw was first used as part of the screw pump of Sennacherib, King of Assyria, for the water systems at the Hanging Gardens of Babylon and Nineveh in the 7th century BC. The Archimedes' screw, Archimedean screw, or screwpump is a Machine historically used for transferring water from a low-lying body of water into Irrigation Sennacherib ( Akkadian Sîn-ahhe-eriba "(moon god Sîn has replaced (lost brothers for me" was the son of Sargon II, whom he Early history The most Neolithic site in Assyria is at Tell Hassuna, the center of the Hassuna culture Tap water ( running water) is part of indoor Plumbing, which became available in the late 19th century and common in the mid-20th century Nineveh ( Akkadian: Ninua; Aramaic: ܢܝܢܘܐ Hebrew נינוה Nīnewē; Arabic نينوى Naīnuwa) The 7th century BC started the first day of 700 BC and ended the last day of 601 BC. ^[3]

The screw was later described by the Greek mathematician Archytas of Tarentum (428 – 350 BC). Greek mathematics, as that term is used in this article is the Mathematics written in Greek, developed from the 6th century BC to the 5th century Archytas (Ἀρχύτας 428 BC – 347 BC was an Ancient Greek Philosopher, Mathematician, Astronomer, Statesman, and strategist Events By place Greece The chief city of Lesbos, Mytilene, revolts against Athenian rule Events By place Persian Empire Sidon, the centre of the revolt against Persia, seeks help from its sister city of Tyre By the 1st century BC, wooden screws were commonly used throughout the Mediterranean world in devices such as oil and wine presses. The 1st century BC started the first day of 100 BC and ended the last day of 1 BC. Wine is an Alcoholic beverage made from the fermentation of Grape juice Metal screws used as fasteners did not appear in Europe until the 1400s.

The metal screw did not become a common woodworking fastener until machine tools for mass production were developed at the end of the eighteenth century. A machine tool is a powered mechanical device typically used to fabricate metal components of machines by Machining, which is the selective removal of metal Mass production (also called flow production, repetitive flow production, series production, or serial production) is the production of In 1770, English instrument maker, Jesse Ramsden (1735-1800) invented the first satisfactory screw-cutting lathe. Jesse Ramsden ( October 6, 1735 – November 5, 1800) was an English astronomical and scientific instrument maker A screw-cutting lathe is a machine (specifically a Lathe) capable of cutting very accurate Screw threads via single-point screw-cutting (which is the process of precisely The British engineer Henry Maudslay (1771-1831) patented a screw-cutting lathe in 1797; a similar device was patented by David Wilkinson in the United States in 1798. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Henry Maudslay ( August 22, 1771 – February 14 1831) was a British Machine tool innovator Tool and die maker Year 1797 ( MDCCXCVII) was a Common year starting on Sunday (link will display the full calendar of the Gregorian calendar (or a Common The name David Wilkinson may refer to David Wilkinson (ambiguity expert (b

In 1908, square-drive screws were invented by Canadian P. L. Robertson, becoming a North American standard. A Robertson screwdriver (also called a square drive screwdriver is a type of Screwdriver with a square -shaped tip with a slight taper (in the same way that flatheads Peter Lymburner Robertson (1879-1951 is a Canadian Inventor of the square-drive screw, first produced in his Milton, Ontario factory In the early 1930s, the Phillips head screw was invented by Henry F. Phillips.

Standardization of screw thread forms accelerated during WWII so that interchangeable parts could be produced by any of the Allied countries. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including

Prior to the mid nineteenth century, cotter pins or pin bolts, and "clinch bolts" (now called rivets), were used in ship building. In the United States cotter pin (also known as a cotter key or a split pin) is a metal Fastener with two tines that are bent during Clinker building is a method of constructing hulls of Boats and Ships by fixing Wooden planks and in the early nineteenth century A rivet is a mechanical Fastener. Before it is installed it consists of a smooth cylindrical shaft with a head on one end

In 1744, the flat-bladed bit for the carpenter's brace was invented, the precursor to the first simple screwdriver. Handheld screwdrivers first appeared after 1800.

Legal issues

In the United States a screw and a bolt have different import duties. For other uses of this word see Tariff (disambiguation. A tariff is a tax imposed on goods when they are moved across a political boundary The difference between them is therefore of keen interest to importers and customs authorities.

This was the subject of a court case Rocknel Fastener, inc v. United States: 34 page PDF. The position is outlined in a current US government document Distinguishing Bolts From Screws: 21 page PDF.

See also

• Screw (simple machine)
• Archimedes' screw
• Nut (hardware)
• Thread pitch gauge
• Thread repair insert
• Tap and die
• Screw thread
• Screw propulsion
• Gender of connectors and fasteners
• Screw-cutting lathe

References

• (1988) in Henry H. Look up SpecialSearch/{{lcscrew}}}}}|{{{2|{{{1|screw}}}}}} The Archimedes' screw, Archimedean screw, or screwpump is a Machine historically used for transferring water from a low-lying body of water into Irrigation A nut is a type of Hardware Fastener with a threaded hole Nuts are almost always used opposite a mating bolt to fasten a stack of parts together Threading gauges, pictured on the right are also referred to as pitch gauges and are used to measure the pitch or lead of Screw threads Thread repair inserts are fastener elements used for one of two purposes To repair a Stripped threaded hole Taps and dies are cutting tools used to create Screw threads in solid substances including but not limited to Metal, Wood, and Plastic. A screw thread is a helical or tapered structure used to convert between rotational and linear movement or force "Screw propulsion" may also refer to propeller propulsion In Electrical and mechanical trades and manufacturing each of a pair of mating connectors or Fasteners is conventionally assigned the designation male A screw-cutting lathe is a machine (specifically a Lathe) capable of cutting very accurate Screw threads via single-point screw-cutting (which is the process of precisely Ryffel (ed. ): Machinery's Handbook 23rd Edition. Machinery's Handbook for machine shop and drafting-room a reference book on machine design and shop practice for the mechanical engineer draftsman toolmaker and New York: Industrial Press Inc. ISBN 0-8311-1200-X.  
• Rybczynsky, Witold (2000). One Good Turn: A Natural History of the Screwdriver and the Screw. Toronto, ON, Canada: Harper Collins. ISBN 0-00-638603-2.  

External links

• Lara Tools screw types - Specialty tool dealer documents more than two dozen different screw heads, along with their drivers.
• Nut and Bolt information charts - Bolt grade markings and strength chart, metric and imperial from Bolt Depot.
• American Fastener - A series of technical documents from an industrial fastener supplier
• Efunda and Metrication.com provide tables for metric screw dimensions. Dimensions of the pitch versions are also available on the websites.
• Socket Head Cap Screw - Interactive Dimension Workform
• Spanner Jaw Sizes Additional background information and spanner jaw size table.
• History of screw recesses from the makers of the ttap-drive fasteners. Star key redirects here For the key on a telephone keyboard see Asterisk.
• UNICOIL - Manufacturer of thread repair system, wire thread inserts, wire insert thread repair taps, inserting tools, thread repair kits.
• Bolted Joints and Threaded Fasteners Technical analysis of screw dynamics
• DANotes: Threaded Fasteners: Mechanics Another technical treatment of screws.
• Power Screws A technical treatment directed especially for power screws. Also discusses efficiency, etc.

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