Bolt (fastener)

Last updated April 18, 2024

Bolt with a nut Bolt-with-nut.jpg — Bolt with a nut

A bolt is an externally helical threaded fastener that fastens objects with unthreaded holes together. This is done by applying a twisting force (torque) to a matching nut. The bolt has an external male thread requiring a matching nut with a pre-formed female thread.^[1] Unlike a screw, which holds objects together by the restricting motion parallel to the axis of the screw via the normal and frictional forces between the screw's external threads and the internal threads in the objects to be fastened, a bolt prevents that linear motion via the frictional and normal forces between the bolt's external threads and the internal threads of the matching nut (not objects to be fastened, which is what allows the bolt to secure objects with unthreaded holes), which can be tightened by applying a torque which moves the nut linearly along the axis of the bolt and compresses the objects to be fastened.

Bolts vs. screws

The distinction between a bolt and a screw is poorly defined. The academic distinction, per Machinery's Handbook ,^[2] is in their intended purpose: bolts are designed to pass through an unthreaded hole in a component and be fastened with the aid of a nut. Screws in contrast are used in components which contain their own thread, or to cut its own internal thread into them. This definition allows ambiguity in the description of a fastener depending on the application it is actually used for, and the terms screw and bolt are widely used by different people or in different countries to apply to the same or varying fastener.

Bolts are often used to make a bolted joint. This is a combination of the nut applying an axial clamping force and also the shank of the bolt acting as a dowel, pinning the joint against sideways shear forces. For this reason, many bolts have a plain unthreaded shank (called the grip length), as this makes for a better, stronger dowel. The presence of the unthreaded shank has often been given as characteristic of bolts vs. screws,^[3]^{[ verification needed ]} but this is incidental to its use, rather than defining.^{[ citation needed ]}

Where a fastener forms its own thread in the component being fastened, it is called a screw.^[2] This is most obviously so when the thread is tapered (i.e. traditional wood screws), precluding the use of a nut,^[2] or when a sheet metal screw or other thread-forming screw is used. A screw must always be turned to assemble the joint. Many bolts are held fixed in place during assembly, either by a tool or by a design of non-rotating bolt, such as a carriage bolt, and only the corresponding nut is turned.^[2]

Bolt heads

Bolts use a wide variety of head designs, as do screws. These are designed to engage with the tool used to tighten them. Some bolt heads instead lock the bolt in place, so that it does not move and a tool is only needed for the nut end.

Common bolt heads include hex, slotted hex washer, and socket cap.

The first bolts had square heads, formed by forging. These are still found, although much more common today is the hexagonal head. These are held and turned by a spanner or socket, of which there are many forms. Most are held from the side, some from in-line with the bolt. Other bolts have T-heads and slotted heads. ^[4]

Many bolts use a screwdriver head fitting, rather than an external wrench. Screwdrivers are applied in-line with the fastener, rather than from the side. These are smaller than most wrench heads and cannot usually apply the same amount of torque. It is sometimes assumed that screwdriver heads imply a screw and wrenches imply a bolt, although this is incorrect. Coach screws, or lag screws, for example, are large square-headed screws with a tapered wood screw thread, used for attaching ironwork to timber. Head designs that overlap both bolts and include the Allen, Torx, hexagonal and splined heads. These modern designs span a large range of sizes and can carry a considerable torque. Threaded fasteners with screwdriver-style heads are often referred to as machine screws whether they are being used with a nut or not.^{[ citation needed ]}

Bolt types

Anchor bolt - Bolt designed to allow objects to be attached to concrete. The bolt head is usually placed in concrete before it has cured or placed before the concrete is poured, leaving the threaded end exposed.
Arbor bolt - Bolt with a washer permanently attached and reversed threading. Designed for use in miter saw and other tools to auto tighten during use to prevent blade fall out.
Carriage bolt - Bolt with a smooth rounded head and a square section to prevent turning followed with a threaded section for a nut.
Elevator bolt - Bolt with a large flat head used in conveyor system setups.
Hanger bolt - Bolt that has no head, machine threaded body followed by a wood threaded screw tip. Allow nuts to be attached to what is really a screw.
Hex bolt - Bolt with a hexagonal head and threaded shank. Section immediately under head may be unthreaded for fastening thicker materials.
J bolt - Bolt shaped like the letter J, used for tie downs. Only the straight section is threaded for a nut.
Rock bolt - Used in tunnel construction to stabilize walls.
Sex bolt or Chicago bolt - Bolt that has a male and female part with interior threads and bolt heads on either end. Commonly used in paper binding.
Shoulder bolt or stripper bolt - Bolt with a broad smooth shank and small threaded section at the end used as a pivot pin or attachment point.
U-bolt - Bolt shaped like the letter U where the two straight sections are threaded. A straight metal plate with two bolt holes is used with nuts to hold pipes or other round objects to the U-bolt.

Bolt materials

Depending on required strength and circumstances, there are several material types can be used for fasteners.^[5]

Steel fasteners (grade 2,5,8) - the level of strength
Stainless steel fasteners (martensitic stainless steel, austenitic stainless steel),
Bronze and brass fasteners - water proof usage
Nylon fasteners - used for the light material and water proof usage.

In general, steel is the most commonly used material of all fasteners: 90% or more.^{[ citation needed ]}

Bolted joints

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.^[6] Structural bolts replaced rivets due to the 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 pre-tension. 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 (and more common type) of 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 lightweight 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.^{[ citation needed ]}

Related Research Articles

A screwdriver is a tool, manual or powered, used for turning screws.

A torque wrench is a tool used to apply a specific torque to a fastener such as a nut, bolt, or lag screw. It is usually in the form of a socket wrench with an indicating scale, or an internal mechanism which will indicate when a specified (adjustable) torque value has been reached during application.

<span class="mw-page-title-main">Fastener</span> Hardware device that mechanically joins or affixes two or more objects together

A fastener or fastening is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or dismantled without damaging the joining components. Steel fasteners are usually made of stainless steel, carbon steel, or alloy steel.

A bolted joint is one of the most common elements in construction and machine design. It consists of a male threaded fastener that captures and joins other parts, secured with a matching female screw thread. There are two main types of bolted joint designs: tension joints and shear joints.

A clevis fastener is a two-piece fastener system consisting of a clevis and a clevis pin head. The clevis is a U-shaped piece that has holes at the end of the prongs to accept the clevis pin. The clevis pin is similar to a bolt, but is either partially threaded or unthreaded with a cross-hole for a split pin. A tang is a piece that is sometimes fitted in the space within the clevis and is held in place by the clevis pin. The combination of a simple clevis fitted with a pin is commonly called a shackle, although a clevis and pin is only one of the many forms a shackle may take.

A socket wrench is a type of spanner that uses a closed socket format, rather than a typical open wrench/spanner to turn a fastener, typically in the form of a nut or bolt.

In general, a spacer is a solid material used to separate two parts in an assembly. Spacers can vary in size from microns to centimeters. They can be made of metal, plastic, glass, and other materials. Shapes include flat sheet, cylindrical and spherical.

In American English, a set screw is a screw that is used to secure an object, by pressure and/or friction, within or against another object, such as fixing a pulley or gear to a shaft. A set screw is normally used without a nut, being screwed instead in a threaded hole drilled in only one of the two objects to be secured. A set screw is often headless and threaded along its entire length, so that it will sit entirely inside that hole; in which case it may be called a grub screw or blind screw.

<span class="mw-page-title-main">Lug nut</span> Fastener, specifically a nut, used to secure a wheel on a vehicle

A lug nut or wheel nut is a fastener, specifically a nut, used to secure a wheel on a vehicle. Typically, lug nuts are found on automobiles, trucks (lorries), and other large vehicles using rubber tires.

An impact wrench is a socket wrench power tool designed to deliver high torque output with minimal exertion by the user, by storing energy in a rotating mass, then delivering it suddenly to the output shaft. It was invented by Robert H. Pott of Evansville, Indiana.

The screw is a mechanism that converts rotational motion to linear motion, and a torque to a linear force. It is one of the six classical simple machines. The most common form consists of a cylindrical shaft with helical grooves or ridges called threads around the outside. The screw passes through a hole in another object or medium, with threads on the inside of the hole that mesh with the screw's threads. When the shaft of the screw is rotated relative to the stationary threads, the screw moves along its axis relative to the medium surrounding it; for example rotating a wood screw forces it into wood. In screw mechanisms, either the screw shaft can rotate through a threaded hole in a stationary object, or a threaded collar such as a nut can rotate around a stationary screw shaft. Geometrically, a screw can be viewed as a narrow inclined plane wrapped around a cylinder.

A sex bolt is a type of fastener comprising a mated pair of screw and post, which are a machine screw and a nut that is barrel-shaped. The nut has a flange and a protruding boss that is internally threaded. The bolt sits within the components being fastened, and the flange provides the bearing surface.

Anchor bolts are used to connect structural and non-structural elements to concrete. The connection can be made by a variety of different components: anchor bolts, steel plates, or stiffeners. Anchor bolts transfer different types of load: tension forces and shear forces.

A jam nut is a low profile type of nut, typically half as tall as a standard nut. It is commonly used as a type of locknut, where it is "jammed" up against a standard nut to lock the two in place. It is also used in situations where a standard nut would not fit.

<span class="mw-page-title-main">Screw</span> Type of fastener characterized by a thread wrapped around a cylinder core

A screw is an externally helical threaded fastener capable of being tightened or released by a twisting force (torque) to the head. The most common uses of screws are to hold objects together and there are many forms for a variety of materials. Screws might be inserted into holes in assembled parts or a screw may form its own thread. The difference between a screw and a bolt is that the latter is designed to be tightened or released by torquing a nut.

A nut is a type of fastener with a threaded hole. Nuts are almost always used in conjunction with a mating bolt to fasten multiple parts together. The two partners are kept together by a combination of their threads' friction, a slight stretching of the bolt, and compression of the parts to be held together.

A dental torque wrench or restorative torque wrench is a torque wrench used to precisely apply a specific torque to a fastener bolt for fixation of an abutment, dentures or prosthetics on a dental implant.

A hex key is a simple driver for bolts or screws that have heads with internal hexagonal recesses (sockets).

Amount of the no-load tension in the bolted joint (preload) greatly affects the reliability of the joint. Multiple techniques exist for preload control to ensure that the tension in the bolt is close to the one specified in the design :

References

↑ "Bolt | Definition of Bolt by Merriam-Webster". Merriam-webster.com. Retrieved 11 April 2016.
1 2 3 4 Machinery's Handbook (21 ed.). New York: Industrial Press. 1980. p. 1131.
↑ Dyke's Automobile and Gasoline Engine Encyclopedia. A. L. Dyke. 1919. p. 701. ISBN 9780140806137. sae uss screw standard.
↑ "What is a bolt?". AALL American Fasteners. Archived from the original on 18 March 2017. Retrieved 13 February 2017.
↑ "Fastener Material Selection". ThomasNet.com.
↑ American Institute of Steel Construction; American Institute of Steel Construction, eds. (2005). Steel construction manual (13 ed.). Chicago, Ill.: American Institute of Steel Construction. ISBN 978-1-56424-055-2.

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[1] "Bolt | Definition of Bolt by Merriam-Webster". Merriam-webster.com. Retrieved 11 April 2016.

[MH,_21,_1132-2] 1 2 3 4 Machinery's Handbook (21 ed.). New York: Industrial Press. 1980. p. 1131.

[dyke-3] Dyke's Automobile and Gasoline Engine Encyclopedia. A. L. Dyke. 1919. p. 701. ISBN 9780140806137. sae uss screw standard.

[4] "What is a bolt?". AALL American Fasteners. Archived from the original on 18 March 2017. Retrieved 13 February 2017.

[5] "Fastener Material Selection". ThomasNet.com.

[6] American Institute of Steel Construction; American Institute of Steel Construction, eds. (2005). Steel construction manual (13 ed.). Chicago, Ill.: American Institute of Steel Construction. ISBN 978-1-56424-055-2.

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