A bolt is an externally helical threaded fastener capable of being tightened or released by 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]
A bolt is an externally helical threaded fastener capable of being tightened or released by 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]
Nuts and bolts were originally hand-crafted together, so that each nut matched its own bolt, but they were not interchangeable. This made it virtually impossible to replace lost or damaged fixers, as they were all different. Joseph Whitworth in 1841 proposed that a standard should be set, but it did not happen immediately.
In 1851 the Great Exhibition of the Works of Industry of All Nations was to be held in Hyde Park, London, England, and it was decided to build the Crystal Palace as part; this had to be done in 190 days, and at reasonable cost. Research into the remains of the destroyed building in 2024 revealed a major innovation that made this possible. The construction firm responsible, Fox Henderson, decided to use nuts and bolts, but to use standardised sizes, a revolutionary method at the time. This enabled the building to be completed in time. The use of interchangeable nuts and bolts was so successful that the Whitworth standard was widely adopted. A British standard was not formally adopted until 1905. [2]
The distinction between a bolt and a screw is poorly defined. The academic distinction, per Machinery's Handbook , [3] 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. In British terminology, a cap screw is a bolt that has threads all the way to the head.
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, [4] [ 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. [3] This is most obviously so when the thread is tapered (i.e. traditional wood screws), precluding the use of a nut, [3] 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. [3]
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. [5]
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. [6]
Depending on required strength and circumstances, there are several material types can be used for fasteners. [7]
In general, steel is the most commonly used material of all fasteners: 90% or more. [8]
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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. [9] 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 ]
Torx is a trademark for a type of screw drive characterized by a 6-point star-shaped pattern, developed in 1967 by Camcar Textron. A popular generic name for the drive is star, as in star screwdriver or star bits. The official generic name, standardized by the International Organization for Standardization as ISO 10664, is hexalobular internal. This is sometimes abbreviated in databases and catalogs as 6lobe. Torx Plus,Torx Paralobe and Torx ttap are improved head profiles.
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 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 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.
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.
An impact driver is a tool that delivers a strong, sudden rotational force and forward thrust. The force can be delivered either by striking with a hammer in the case of manual impact drivers, or mechanically in the case of powered impact drivers.
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.
Computer case screws are the hardware used to secure parts of a PC to the case. Although there are numerous manufacturers of computer cases, they have generally used three thread sizes. The Unified Thread Standard (UTS) originates from the United States, while the ISO metric screw thread is standardized worldwide. In turn, these thread standards define preferred size combinations that are based on generic units—some on the inch and others on the millimetre.
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.
An insert nut provides a threaded socket for a wooden workpiece, similar to a wall anchor. Insert nuts are inserted into a pre-drilled hole by one of two means: screw in and hammer in. In both cases, the external protrusions bite into the wood, preventing the nut from either turning or pulling out.
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.
ASTM A325 is an ASTM International standard for heavy hex structural bolts, titled Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength. It defines mechanical properties for bolts that range from 1⁄2 to 1+1⁄2 inches in diameter.
A nutdriver or nut driver is a hand tool for tightening or loosening nuts and bolts. It essentially consists of a socket attached to a shaft and cylindrical handle and is similar in appearance and use to a screwdriver. They generally have a hollow shaft to accommodate a shank onto which a nut is threaded. They are typically used for lower torque applications than wrenches or ratchets and are frequently used in the appliance repair and electronics industries.
A hex key is a simple driver for bolts or screws that have heads with internal hexagonal recesses (sockets).
Width across flats is the distance between two parallel surfaces on the head of a screw or bolt, or a nut, mostly for torque transmission by positive locking.
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