screw or bolt is a type of fastener characterized by a helix ridge, known as an external threador just [[Screw thread|thread]] wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an .... Read More

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# Differentiation between bolt and screw

File Bolt (PSF).png File DIN6914 UNI5587.jpg There is no universally accepted distinction between a screw and a bolt. [[Machinerys Handbook]] describes the distinction as follows: }} This distinction is consistent with ASME B18.2.1 and some dictionary definitions for screwlt;ref>lt;/ref>lt;/ref> and boltlt;/ref>lt;/ref>lt;/ref> The issue of what is a screw and what is a bolt is not completely resolved with Machinerys Handbook distinction, however, because of confounding terms, the ambiguous nature of some parts of the distinction, and usage variations.lt;/ref>Some of these issues are discussed below:

## Machine screws

ASME standards specify a variety of "Machine Screws" in diameters ranging up to These fasteners are often used with nuts as well as driven into tapped holes. They might be considered a screw or a bolt based on the Machinerys Handbook distinction. In practice, they tend to be mostly available in smaller sizes and the smaller sizes are referred to as screws or less ambiguously as machine screws, although some kinds of machine screw can be referred to as stove bolts.

## Hex cap screws

ASME standard B18.2.1-1996 specifies Hex Cap Screws that range in size from in diameter These fasteners are very similar to hex bolts. They differ mostly in that they are manufactured to tighter tolerances than the corresponding bolts. Machinerys Handbook refers parenthetically to these fasteners as "Finished Hex Bolts". Reasonably, these fasteners might be referred to as bolts, but based on the US government document Distinguishing Bolts from Screws the US government might classify them as screws because of the tighter tolerance.lt;/ref> In 1991 responding to an influx of counterfeit fasteners Congress passed PL 101-592http://ts.nist.gov/WeightsAndMeasures/fqaregs2.cfm Fastener Quality Act (FQA): Text of the Fastener Quality Act - fqaregs2] "Fastener Quality Act" This resulted in the rewriting of specifications by the ASME B18 committee. B18.2.1http://catalog.asme.org/Codes/PrintBook/B1821_1996_Square_Hex_Bolts.cfm B18.2.1 - 1996 Square and Hex Bolts and Screws, Inch Series - Print-Book] was re-written and as a result they eliminated the "Finished Hex Bolts" and renamed them the "Hex Cap Screw"—a term that had existed in common usage long before, but was now also being codified as an official name for the ASME B18 standard.

## Lug bolts and head bolts

These terms refer to fasteners that are designed to be threaded into a tapped hole that is in part of the assembly and so based on the Machinerys Handbook distinction they would be screws. Here common terms are at variance with Machinerys Handbook distinction.lt;/ref>lt;/ref>

## Lag screw

File Lag screws aka lag bolts 001.png File Lag screws aka lag bolts 002.png Lag screws, also sometimes called lag bolts, are basically "large wood screws". Square lag screws and hex lag screws are covered by ASME B18.2.1. A typical lag bolt can range in diameters from 1/4" to 1 1/4", and lengths from 1/4" to 6" or longer, with coarse threads of a wood-screw or sheet-metal-screw threadform (but larger). The head is typically an external hex. The materials are usually carbon steel substrate with a coating of zinc galvanization (for corrosion resistance). The zinc coating may be bright (electroplated), yellow (electroplated), or dull gray hot-dip galvanizing Lag bolts are used to lag together lumber framing, to lag machinery feet to wood floors, and other heavy carpentry applications. These fasteners are clearly "screws" when defined by the Machinerys Handbook distinction. The term "lag bolt" has been replaced by "lag screw" in the Machinerys Handbook. However, in the minds of most tradesmen, they are "bolts", simply because they are large, with hex or square heads. In the United Kingdom, lag bolts/screws are known as coach screwsthough this can also refer to carriage bolts (round head).

## Government standards

The US government made an effort to formalize the difference between a bolt and a screw because different tariffs apply to each.lt;/ref> The document seems to have no significant effect on common usage and does not eliminate the ambiguous nature of the distinction between screws and bolts for some threaded fasteners. The document also reflects (although it probably did not originate) significant confusion of terminology usage that differs between the legal/statutory/regulatory community and the fastener industry. The legal/statutory/regulatory wording uses the terms "coarse" and "fine" to refer to the tightness of the engineering tolerance range, referring basically to "high-quality" or "low-quality", but this is a poor choice of terms, because those terms in the fastener industry have a different meaning (referring to Screw thread Coarse versus fine .

## Historical issue

Old United States Standard and Society of Automotive Engineers standards defined cap screws as fasteners with shanks that were threaded to the head and bolts as fasteners with shanks that were partially unthreaded.lt;/ref> The relationship of this rule to the idea that a bolt by definition takes a nut is clear (because the unthreaded section of the shank, which is called the grip was expected to pass through the substrate without threading into it). This is now an obsolete distinction.

## Controlled vocabulary versus natural language

The distinctions above are enforced in the controlled vocabulary of standards organization . Nevertheless, there are sometimes differences between the controlled vocabulary and the natural language use of the words by machinists, auto mechanics and others. These differences reflect linguistic evolution shaped by the History of technology The words boltand screwhave both existed since before todays modern mix of fastener types existed, and the natural usage of those words has evolved retronym usly in response to the technological change. (That is, the use of words as names for objects changes as the objects themselves change.) Non-threaded fasteners predominated until the advent of practical, inexpensive screw-cutting in the early 19th century. The basic meaning of the word screwhas long involved the idea of a helical screw thread, but the Archimedes screw and the screw gimlet (tool) (like a corkscrew) preceded the fastener. The word boltis also a very old word, and it was used for centuries to refer to metal rods that passed through the substrate to be fastened on the other side, often via nonthreaded means (clinching, forge welding, pinning, wedging, etc.). The connection of this sense to the sense of a door bolt or the crossbow bolt is apparent. In the 19th century, bolts fastened via screw threads were often called screw boltsin contradistinction to Clinker (boat building) Fastening the centre-line structure In common usage, the distinction (not rigorous) is often that screws are smaller than bolts, and that screws are generally tapered while bolts are not. For example, cylinder head bolts are called "bolts" (at least in North American usage) despite the fact that by some definitions they ought to be called "screws". Their size and their similarity to a bolt that would take a nut seem linguistically to overrule any other factors in this natural language word choice proclivity.

## Other distinctions

Bolts have been defined as headed fasteners having external threads that meet an exacting, uniform bolt thread specification (such as ISO metric screw thread M, MJ, Unified Thread Standard UN, UNR, and UNJ) such that they can accept a non-tapered nut. Screws are then defined as headed, externally threaded fasteners that do not meet the above definition of bolts.lt;!-- See the talk page. --> These definitions of screw and bolt eliminate the ambiguity of the Machinerys handbook distinction. And it is for that reason, perhaps, that some people favor them. However, they are neither compliant with common usage of the two words nor are they compliant with formal specifications. I offer that a screw is designed to cut its own thread, it has no need for access from or exposure to the side of the component being fastened to. This definition of screw would be further reinforced by the consideration of the developments of fasteners such as Tek Screws for roof cladding, self-drilling & self-tapping screws for various metal fastening applications, roof batten screws to reinforce the connection between the roof batten and the rafter, decking screws etc.. A bolt on the other hand is the male part of a fastener system designed to be accepted by a pre-equipped socket of exactly the same thread design. RPA

# Types of screw and bolt

lt;!-- Carriage bolt redirects here --> Threaded fasteners either have a tapered shank or a non-tapered shank. Fasteners with tapered shanks 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 shank are designed to mate with a nut or to be driven into a tapped hole.

## Fasteners with a tapered shank (self-threading screws)

| class"wikitable sortable" |- ! class"unsortable" | !!style"width: 140px" | American name !!style"width: 140px" | British name !! class"unsortable" | Description |- | || chipboard screw
particle board screw || || Similar to a drywall screw except that it has a thinner shaft and provides better resistance to pull-out in particle board, while offset against a lower shear strength. The threads on particle board screws are asymmetrical. |- | || lt;br />Tapcons
masonry screw
confast screw
blue screw
self-tapping screw
Titen || || A stainless or carbon steel screw for fastening wood, metal, or other materials into concrete or masonry. Concrete screws are commonly blue in color, with or without corrosion coating.Source: http://www.confast.com/articles/tapcon-screw.aspx They may either have a Phillips flat head or a slotted hex washer head. Heads sizes range from and lengths from Typically an installer uses a hammer drill to make a pilot hole for each concrete screw. |- | || deck screw || || Similar to drywall screw except that it has improved corrosion resistance and is generally supplied in a larger gauge. Most deck screws have a type-17 (auger type) thread cutting tip for installation into decking materials. They have bugle heads that allows the screw to depress the wood surface without breaking it. |- | File Stockschraube.jpg lt;!-- I know its not quite right because one end has a machine thread on it, but its close enough until a better image is taken --> || double ended screw
dowel screw
hanger bolt || || Similar to a wood screw but with two pointed ends and no head, used for making hidden joints between two pieces of wood.
A hanger bolt has wood screw threads on one end and machine threads on the other. A hanger bolt is used when it is necessary to fasten a metal part to a wood surface. |- | File Screw.agr.jpg || 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. |- | File Eye bolt wood thread.jpg || eye screw
screw eye || || Screw with a looped head. Larger ones are sometimes called lag eye screws. Designed to be used as attachment point, particularly for something that is hung from it. |- | File Tire-fond cropped.JPG || lag bolt

## Fasteners with a non-tapered shank

Teks 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. The points are numbered from 1 through 5, the larger the number, the thicker metal it can go through without a pilot hole. A 5 point can drill a of steel, for example. |- | File Vis-auto-taraudeuse.jpeg || self-tapping machine screw || || A self-tapping machine screw is similar to a machine screw except the lower part of the shank is designed to cut threads as the screw is driven into an untapped hole. The advantage of this screw type over a self-drilling screw is that, if the screw is reinstalled, new threads are not cut as the screw is driven. |- | || set bolt || tap bolt || A bolt that is threaded all the way to the head. An ASME B18.2.1 compliant set/tap bolt has the same tolerances as an ASME B18.2.1 compliant hex cap screw. |- | File Setscrews (PSF).png || set screw || grub screw || A set screw is 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. The most often used type is the socket set screw, which is tightened or loosened with a hex key. |- | || shoulder bolt

## Fasteners with built in washers

A fastener with a built in Washer (hardware) is called a SEM or SEMS, short for pre-asSEM led.lt;/ref>lt;/ref> It could be fitted on either a tapered or non-tapered shank.

## Superbolt, or multi-jackbolt tensioner

A superbolt, or multi-jackbolt tensioner is an 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. Because of this, the amount of torque required to achieve a given preload is reduced. 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 or hanger bolt

A hanger screw is 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 to tables. Also known as a dowel screw.

# Materials

Screws and bolts are usually made of steel Where great resistance to weather or corrosion is required, like in very small screws or medical implants, materials such as stainless steel brass titanium bronze silicon bronze or monel may be used. Galvanic corrosion of dissimilar metals can be prevented (using aluminium screws for double-glazing tracks for example) by a careful choice of material. Some types of plastic, such as nylon or polytetrafluoroethylene (PTFE), can be threaded and used for fastenings requiring moderate strength and great resistance to corrosion or for the purpose of electrical Electrical insulation Often a surface coating is used to protect the fastener from corrosion (e.g. bright zinc plating for steel screws), to impart a decorative finish (e.g. japanning or otherwise alter the surface properties of the base material. Selection criteria of the screw materials include: size, required strength, resistance to corrosion, joint material, cost and temperature.

# Bolted joints

File Rustybolt th.jpg The American Institute of Steel Construction (AISC 13th Edition Steel Design Manual section 16.1 chapter J-3 specifies the requirements for bolted structural connections. Structural bolts replaced rivets due to decreasing cost and increasing strength of structural bolts in the 20th century. Connections are formed with two types of joints: slip-critical connections and bearing connections. In slip-critical connections, movement of the connected parts is a serviceability condition and bolts are tightened to a minimum required pretension. Slip is prevented through friction of the "faying" surface, that is the plane of shear for the bolt and where two members make contact. Because friction is proportional to the normal force, connections must be sized with bolts numerous and large enough to provide the required load capacity. However, this greatly decreases the shear capacity of each bolt in the connection. The second type and more common connection is a bearing connection. In this type of connection the bolts carry the load through shear and are only tightened to a "snug-fit". These connections require fewer bolts than slip-critical connections and therefore are a less expensive alternative. Slip-critical connections are more common on flange plates for beam and column splices and moment critical connections. Bearing type connections are used in light weight structures and in member connections where slip is not important and prevention of structural failure is the design constraint. Common bearing type connections include: shear tabs, beam supports, gusset plates in trusses.

# Mechanical classifications

## Inch

SAE J429 defines the bolt grades for inch-system sized bolts and screws. It defines them by grade which ranges from 0 to 8, with 8 being the strongest. Higher grades do not exist within the specification.lt;/ref> SAE grades 5 and 8 are the most common. | class"wikitable collapsible collapsed" width"100%" border"1" style"text-align:center" ! colspan10 | Head markings and properties for inch-system hex-head cap screwslt;/ref> |- !rowspan2| Head marking !rowspan2| Grade, material and condition !rowspan2| Nominal size range (in) !colspan2| ultimate tensile strength !colspan2| Yield strength, min. !colspan2| Tensile strength, min. !rowspan2| Core hardness (Rockwell scale |- !ksi!!MPa !ksi!!MPa !ksi!!MPa |- | rowspan6 | File Hex cap screw-no markings.svg | SAE Grade 0 lt;ref name"siu"/> | colspan8 | Strength and hardness is not specified |- | SAE grade 1 lt;br />ASTM A307 lt;ref name"fastspec">lt;/ref>
Low carbon steel | 1- | | colspan2| | | B70–100 |- | ASTM A307 - Grade B lt;ref name"fastspec"/>
Low or medium carbon steel | 4 | colspan2| | colspan2| | alignright|60 minimum
100 maximum | alignright|410 minimum
690 maximum | B69–95 |- | rowspan2 | SAE grade 2 lt;br />Low or medium carbon steel | | | | | B80–100lt;/ref> |- | Greater than | | | | B70–100 |- | SAE grade 4 lt;ref name"american">lt;/ref>
Medium carbon steel; cold worked | 1- | colspan2| | | | |- | File Hex cap screw-grade 3.svg || SAE grade 3 lt;ref name"fastspec"/>
Medium carbon steel; cold worked || 1 | | colspan2| | | B70–100 |- | rowspan4 | File Hex cap screw-grade 5.svg || rowspan2 | SAE grade 5 lt;br />Medium carbon steel; quench and tempered | 1 (inc.) | | | | C25–34 |- | 1–1- | | | | C19–30 |- | rowspan2 | ASTM A449 - Type 1 lt;ref name"fastspec"/>
Medium carbon steel; quench and tempered || 1–1-(inc.) | | colspan2| | | C19–30 |- | 1-3 | | colspan2| | | Brinell scale 183–235 |- | File Hex cap screw-grade 5.1.svg || SAE grade 5.1 lt;ref name"itp">lt;/ref>
Low or medium carbon steel; quench and tempered || No. 6– | | colspan2| | | C25–40 |- | rowspan2 | File Hex cap screw-grade 5.2.svg || SAE grade 5.2 lt;ref name"itp"/>
Low carbon martensitic steel; quench and tempered || rowspan2 | 1 | rowspan2 |85 | rowspan2 |590 | rowspan2 colspan2| | rowspan2 |120 | rowspan2 |830 | C26–36 |- | ASTM A449 - Type 2 lt;ref name"itp"/>
Low carbon martensitic steel; quench and tempered || C25–34 |- | rowspan2 | File Hex cap screw-ASTM A325.svg r File Hex cap screw-ASTM A325 lines.svg || rowspan2 | [[ASTM A325]] - Type 1 lt;ref name"fastspec"/>
Medium carbon steel; quench and tempered || 1 (inc.) | | lt;ref name"american"/> | | C24–35 |- | 1–1- | | lt;ref name"american"/> | | C19–31 |- | rowspan2 | File Hex cap screw-ASTM A325 type 3.svg lt;ref name"crnote">Other markings may be used to denote atmospheric corrosion resistant material
|| rowspan2 | ASTM A325 - Type 3 lt;ref name"fastspec"/>
Atmospheric corrosion resistant steel; quench and tempered || 1 | | lt;ref name"american"/> | | C24–35 |- | 1–1- | | lt;ref name"american"/> | | C19–31 |- | rowspan2 | File Hex cap screw-ASTM A354 grade BC.svg || rowspan2 | [[ASTM A354]] - Grade BC lt;ref name"fastspec"/>
Medium carbon alloy steel; quench and tempered || 2-(inc.) | | lt;ref name"american"/> | | C26–36 |- | 2-4 | | lt;ref name"american"/> | | C22–33 |- | File Hex cap screw-grade 7.svg || SAE grade 7 lt;br />Medium carbon alloy steel; quench and tempered || 1- | | | | |- | File Hex cap screw-grade 8.svg || SAE grade 8 lt;br />Medium carbon alloy steel; quench and tempered || 1- | | | | C32–38 |- |File Hex cap screw-ASTM A354 grade BD lines.svg || rowspan2 | ASTM A354 - Grade BD lt;ref name"Fastenal">lt;/ref> || 2-(inc.) | | lt;ref name"Fastenal"/> | | C33–39 |- | File Hex cap screw-ASTM A354 grade BD.svg || 2-4 | | lt;ref name"Fastenal"/> | | C31–39 |- | File Hex cap screw-grade 8.2.svg || SAE grade 8.2 lt;ref name"johndeere"/>
Medium carbon boron martensitic steel; fully kilned, fine grain, quench and tempered || 1 | | colspan2| | | C33–39 |- | File Hex cap screw-ASTM A490.svg | [[ASTM A490]] - Type 1 lt;ref name"fastspec"/>
Medium carbon alloy steel; quench and tempered | rowspan2 | 1- | rowspan2 alignright |120 | rowspan2 alignright |830 | rowspan2 alignright |130 | rowspan2 alignright |900 | rowspan2 alignright|150 minimum
170 maximum | rowspan2 alignright|1,000 minimum
1,200 maximum | rowspan2 | C33–38 |- | File Hex cap screw-ASTM A490 type 3.svg lt;ref name"crnote"/> | ASTM A490 - Type 3 lt;ref name"fastspec"/>
Atmospheric corrosion resistant steel; quench and tempered |- | rowspan3 | || rowspan3 | 18-8 Stainless lt;br />Stainless steel with | (inc.) |rowspan3 colspan2| |alignright|40 minimum
80–90 typical |alignright|280 minimum
550–620 typical |alignright|100–125 typical |alignright|690–860 typical |rowspan3| |- | 1 (inc.) | rowspan2 alignright|40 minimum
45–70 typical | rowspan2 alignright|280 minimum
310–480 typical |alignright|100 typical |alignright|690 typical |- | over 1 |alignright| 80–90 typical |alignright| 550–620 typical |}

## Metric

The international standard for metric screws is defined by ISO 898 specifically ISO 898-1. SAE J1199 and ASTM F568M are two North American metric standards that closely mimic the ISO standard. In case of inch sizes the grade is dictated by the number of radial shapes plus a value of two. Inch-system bolts use integer values to indicate grades but metric bolts use numbers with one decimal. The two North American standards use the same property class markings as defined by ISO 898. The ASTM standard only includes the following property classes from the ISO standard: 4.6, 4.8, 5.8, 8.8, 9.8, 10.9, and 12.9; it also includes two extra property classes: 8.8.3 and 10.9.3.lt;/ref> ASTM property classes are to be stamped on the top of screws and it is preferred that the marking be raised. | class"wikitable collapsible collapsed" width"100%" border"1" style"text-align:center" ! colspan10 | Head markings and properties for metric hex-head cap screwslt;/ref> |- !rowspan2| Head marking !rowspan2| Grade, material and condition !rowspan2| Nominal size range (mm) !colspan2| Proof strength !colspan2| Yield strength, min. !colspan2| Tensile strength, min. !rowspan2| Core hardness (Rockwell scale |- !MPa!!ksi !MPa!!ksi !MPa!!ksi |- | File Hex cap screw-class 3.6.svg | Class 3.6 lt;ref>lt;/ref> | 1.6–36 | | | | B52–95 |- | File Hex cap screw-class 4.6.svg | Class 4.6 lt;br />Low or medium carbon steel | 5–100 | | | | B67–95 |- | File Hex cap screw-class 4.8.svg | Class 4.8 lt;br />Low or medium carbon steel; fully or partially annealed | 1.6–16 | | | | B71–95 |- | File Hex cap screw-class 5.8.svg | Class 5.8 lt;br />Low or medium carbon steel; cold worked | 5–24 | | | | B82–95 |- | rowspan2 | File Hex cap screw-class 8.8.svg | rowspan2 | Class 8.8 lt;ref name"boltdepot"/>
Medium carbon steel; quench and tempered | Under 16 (inc.) | | | | |- | rowspan3 | 17–72 | rowspan5 alignright |600 | rowspan5 alignright |87 | rowspan5 alignright |660 | rowspan5 alignright |96 | rowspan5 alignright |830 | rowspan5 alignright |120 | rowspan5 | C23–34 |- | File Hex cap screw-class 8.8 line.svg | Class 8.8 low carbon lt;br />Low carbon boron steel; quench and tempered |- | File Hex cap screw-class 8.8.3.svg | Class 8.8.3 lt;ref name"F568M" />
Atmospheric corrosion resistant steel; quench and tempered |- | File Hex cap screw-ASTM A325M 8S.svg | [[ASTM A325M]] - Type 1 lt;ref name"uiowa"/>
Medium carbon steel; quench and tempered | rowspan2 | 12–36 |- | File Hex cap screw-ASTM A325M 8S3.svg | ASTM A325M - Type 3 lt;ref name"uiowa">lt;/ref>lt;/ref>
Atmospheric corrosion resistant steel; quench and tempered |- | File Hex cap screw-class 9.8.svg | Class 9.8 lt;br />Medium carbon steel; quench and tempered | rowspan2 | 1.6–16 | rowspan2 alignright | 650 | rowspan2 alignright | 94 | rowspan2 alignright | 720 | rowspan2 alignright | 104 | rowspan2 alignright | 900 | rowspan2 alignright | 130 | rowspan2 | C27–36 |- | File Hex cap screw-class 9.8 line.svg | Class 9.8 low carbon lt;br />Low carbon boron steel; quench and tempered |- | File Hex cap screw-class 10.9.svg | Class 10.9 lt;br />Alloy steel; quench and tempered | rowspan3 | 5–100 | rowspan5 alignright |830 | rowspan5 alignright |120 | rowspan5 alignright |940 | rowspan5 alignright |136 | rowspan5 alignright |1,040 | rowspan5 alignright |151 | rowspan5 | C33–39 |- | File Hex cap screw-class 10.9 line.svg | Class 10.9 low carbon lt;br />Low carbon boron steel; quench and tempered |- | File Hex cap screw-class 10.9.3.svg | Class 10.9.3 lt;ref name"F568M"/>
Atmospheric corrosion resistant steel; quench and tempered |- |File Hex cap screw-ASTM A490M 10S.svg || [[ASTM A490M]] - Type 1 lt;ref name"uiowa"/>lt;/ref>
Alloy steel; quench and tempered | rowspan2 | 12–36 |- |File Hex cap screw-ASTM A490M 10S3.svg | ASTM A490M - Type 3 lt;ref name"uiowa"/>
Atmospheric corrosion resistant steel; quench and tempered |- | File Hex cap screw-class 12.9.svg | Class 12.9 lt;br />Alloy steel; quench and tempered | 1.6–100 | | | | C38–44 |- | rowspan4 | File Hex cap screw-A2.svg | A2 lt;ref name"boltdepot"/>
Stainless steel with 17–19% chromium and 8–13% nickel | up to 20 | colspan2 rowspan4 | | alignright | 210 minimum
450 typical | alignright | 30 minimum
65 typical | alignright | 500 minimum
700 typical | alignright | 73 minimum
100 typical | rowspan4 | |- | ISO 3506-1 A2-50 Citation needed|dateJune 2009}}
304 stainless steel-class 50 (annealed) | rowspan3 | | | |- | ISO 3506-1 A2-70 Citation needed|dateJune 2009}}
304 stainless steel-class 70 (cold worked) | | |- | ISO 3506-1 A2-80 Citation needed|dateJune 2009}}
304 stainless steel-class 80 | | |}

# {{visible anchor|Types of screw drive}}s

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 in the US; hex, Robertson, and Torx are also common in some applications, and Pozidriv has almost completely replaced Phillips in Europe. 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.

# Tools

File Screw-into-wood.ogg 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 drill may also be used with screw-driving attachments. Where the holding power of the screwed joint is critical, torque-measuring and torque-limiting screwdriversare used to ensure sufficient but not excessive force is developed by the screw. The hand tool for driving hex head threaded fasteners is a spanner(UK usage) or wrench(US usage).

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. Other relatively common systems include the British Standard Whitworth British Association screw threads and the Unified Thread Standard

## Whitworth

A later standard established in the United Kingdom was the British Association (BA) screw threads, named after the British Association for Advancement of Science. Screws were described as "2BA", "4BA" etc., the odd numbers being rarely used, except in equipment made prior to the 1970s 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. BA threads are specified by British Standard BS 93:1951 "Specification for British Association (B.A.) screw threads with tolerances for sizes 0 B.A. to 16 B.A." While not related to ISO metric screws, the sizes were actually defined in metric terms, a 0BA thread having a 6 mm diameter and 1 mm pitch. Other threads in the BA series are related to 0BA in a geometric series with the common factors 0.9 and 1.2. For example, a 4BA thread has pitch $\scriptstyle p0.9^4$ mm (0.65mm) and diameter $\scriptstyle 6p^1.2\right\}$ mm (3.62mm). Although 0BA has the same diameter and pitch as ISO M6, the threads have different forms and are not compatible. BA threads are still common in some niche applications. Certain types of fine machinery, such as moving-coil meters and clocks, tend to have BA threads wherever they are manufactured. BA sizes were also used extensively in aircraft, especially those manufactured in the United Kingdom. BA sizing is still used in railway signalling, mainly for the termination of electrical equipment and cabling. BA threads are extensively used in Model Engineering where the smaller hex head sizes make scale fastenings easier to represent. As a result many UK Model Engineering suppliers still carry stocks of BA fasteners up to typically 8BA and 10BA. 5BA is also commonly used as it can be threaded onto 1/8 rod.

The Unified Thread Standard (UTS) is most commonly used in the United States of America, but is also extensively used in Canada and occasionally in other countries. The size of a UTS screw is described using the following format: X-Y where X is the nominal size (the hole or slot size in standard manufacturing practice through which the shaft of the screw can easily be pushed) and Y is the threads per inch (TPI). For sizes inch and larger the size is given as a fraction; for sizes less than this an integer is used, ranging from 0 to 16. The integer sizes can be converted to the actual diameter by using the formula 0.060 + 0.013 * number. For example, a #4 screw is 0.060 + 0.013 * 4 0.112 inches in diameter. For most size screws there are multiple TPI available, with the most common being designated a Unified Coarse Thread (UNC or UN) and Unified Fine Thread (UNF or UF).

# Other fastening methods

Alternative fastening methods are: * nail (fastener) * rivet * pin (dowel pins, taper pins, roll pins, spring pins, cotter pins) * pinned shafts (keyed shafts, woodruff keys, gibb-headed key) * clinker (boat building) Fastening the centre-line structure * welding * solder ng * brazing * Woodworking joints (mortise & tenon, dovetailing, box joints, lap joints) * gluing * Adhesive tape * clinch fastening.

* Gender of connectors and fasteners * Tap and die ** Die head * Thread angle * Threaded rod (e.g., studs, allthread) * Threading (manufacturing) * Thread pitch gauge * List of screw drives * Syndesmotic screw * Dowel

# References

## Bibliography

* * * * * * * *

* http://screwsnutsbolts.wix.com/screwsnutsbolts How the World Got Screwed] * http://justpaste.it/7ux Screws Small Encyclopedia] * http://hdl.handle.net/2060/19900009424 NASA-RP-1228 Fastener Design Manual] (this link not working) * http://www.baconsdozen.co.uk/tools/conversion%20charts.htm Imperial/Metric fastening sizes comparison] * http://books.google.com/books?id2yADAAAAMBAJ&pgPA149&dqpopular+science+February+1946&hlen&eivOPkTL3jJsnOnAf8toClDQ&saX&oibook_result&ctresult&resnum5&ved0CDMQ6AEwBA#vonepage&qpopular%20science%20February%201946&ftrue "Hold Everything", February 1946, Popular Science"] article section on screws and screw fastener technology developed during World War Two * [http://www.amesweb.info/BoltedJoint/BoltedJointEstimate.aspx Bolted Joint Estimator] {{Woodworking}} [[Category:Metalworking]] [[Category:Screws| ]] [[Category:Woodworking]] {{Link GA|es}}
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