A bolt is a form of threaded fastener with an external male thread requiring a matching pre-formed female thread such as a nut. Bolts are very closely related to screws. Bolts are designed to pass through an unthreaded hole in a component and be fastened with the aid of a nut, although such a fastener can be used without a nut to tighten into a threaded component such as a nut-plate or tapped housing. They 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, but this is incidental to its use, rather than defining.

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. 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 are large square-headed screws with a tapered wood screw thread, used for attaching ironwork to timber. Head designs that overlap both bolts and screws are the Allen or Torx heads; hexagonal or splined sockets. 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. There are many types of bolts, such as hex bolt - Bolt with a hexagonal head and threaded body. Section immediately under head may or may not be threaded; carriage bolt - Bolt with a smooth rounded head and a square section to prevent turning followed with a threaded section for a nut; 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; 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.

Flange bolts have a circular flange under the head that acts like a washer to distribute the load. Flange bolts that are non-serrated are sometimes called frame bolts. A flange bolt differs from the common bolt in that it has a wider surface area under the head to provide for an even distribution of clamping pressure. This wider surface acts like a washer, eliminating the need to combine one with this kind of bolt. Flange bolts are available in numerous sizes, strengths, and configurations. Like most other types of fasteners on the market, metric flange bolts are available for any applications that require them. Specially designed flange bolts are equipped with anti-rotational “teeth” designed to “bite” or dig into the material one might need to fasten together. Similar to the locking rings one might see on a soda bottle or milk jug, these teeth on the flange bolt can be turned backward, but often require more force. This type of design is what makes a flange bolt uniquely and strategically different from a common bolt.

Hexagon socket bolts with cylindrical head are also referred to as hexagon socket bolts, cup-head screws, and hexagon socket screws. The names are different, but the meaning is the same. Commonly used hexagon socket head screws also have 4.8, 8.8, 10.9, and 12.9. Also called hexagon socket screws, also called hexagon socket bolts. Its head is hexagonal and cylindrical. According to the material, there are stainless steel and iron. There are stainless steel SUS202 hexagon socket head cap screws. This is a common stainless steel material. There are stainless steel SUS304 hexagon socket cap screws and stainless steel SUS316 hexagon socket cap screws. The iron is classified according to the strength grade of the hexagon socket head screw. There are 4.8 grade hexagon socket head screws, 8.8 grade hexagon socket head screws, 10.9 grade hexagon socket head screws, and 12.9 grade hexagon socket head screws. Grade 8.8-12.9 hexagon socket head cap screws are called high-strength, high-grade hexagon socket bolts.

Stud bolts, also known as double-headed screws. It is used to connect the fixed link function of the machine. The stud bolt has threads at both ends, and the screw in the middle is thick or thin. Generally used in mining machinery, bridges, automobiles, motorcycles, boiler steel structures, pendant towers, long-span steel structures and large buildings. And square bolts are now most commonly used for aesthetic purposes to provide a rustic look in a new structure or to match existing fasteners in an older structure. Square lag screws are also used for these purposes. Crossarm or machine bolts are commonly supplied for the utility industry and included an added cone point. Expansion bolts can be used to secure heavy objects to walls or floors and handle vertical and horizontal loads. By tightening the bolt, the nut on the opposite end pulls into the shell, expanding it outward and wedging it inside the hole in the wall or floor. It requires a spanner or socket wrench to fasten or undo the bolt and ideal for heavy duty fastening of steel and wood structures walls and floors.

Nuts, parts that are screwed together with bolts or screws for fastening, are a kind of original that must be used in all production and manufacturing machinery. According to different materials, it is divided into several types such as carbon steel, stainless steel, non-ferrous metals (such as copper). Nuts are parts that tightly connect mechanical equipment. Through the inner threads, nuts and bolts of the same specification can be connected together. For example, M4-P0.7 nuts can only be connected with M4-P0.7 series bolts (in the nut). Among them, M4 means the inner diameter of the nut is about 4mm, and 0.7 means that the distance between the two threads is 0.7mm); the same is true for American products, for example, a 1/4-20 nut can only be matched with a 1/4-20 screw ( A 1/4 finger nut has an inner diameter of about 0.25 inches, and 20 fingers have 20 teeth in each inch).

The hexagonal nut is used in conjunction with screws, bolts and screws to connect and fasten parts. Among them, the Type 1 six-purpose nut is the most widely used. The C-level nut is used for machines, equipment or structures with rough surface and low precision requirements; A-level and B-level nuts are used for relatively smooth surfaces and high precision requirements. machine, equipment or structure. The thickness M of the type 2 hexagon nut is thicker, and it is mostly used in occasions where assembly and disassembly are often required. The thickness M of the hexagonal thin nut is relatively thin, and it is mostly used in situations where the surface space of the connected parts is limited.

The flange nut is a nut with a wide flange on one end that acts as an integral washer. This serves to distribute the pressure of the nut over the part being fastened, reducing the possibility of damage to the part and making it less likely to loosen due to uneven tightening surfaces. These nuts are mostly hexagonal in shape and are made of hardened steel, usually plated with zinc.
In many cases, the flange is fixed and turns with the nut. The flanges may be serrated to provide locking. The serrations are angled so that the nut does not rotate in the same direction as the nut is loosened. Because of the serrations, they cannot be used with washers or on scratched surfaces. The serrations help prevent the vibration of the nut from moving the fastener, thus maintaining the retention force of the nut. Flange nuts sometimes feature rotating flanges that help create a more stable structure without affecting the finished product like serrated flange nuts. Swivel flange nuts are mainly used to join wood and plastic. Sometimes both sides of the nut are serrated, allowing either side to lock. Self-aligning nuts have male spherical flanges that mate with female dish washers to allow the nut to tighten on surfaces that are not perpendicular to the nut. A spring cushion is installed under the nut to prevent the nut from loosening.