Fasteners are a wide range of mechanical parts used for fastening connections. They are used in a broad range of industries, including energy, electronics, electrical appliances, machinery, chemicals, metallurgy, mold making, and hydraulics. Various types of fasteners can be found on all kinds of machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, chemicals, meters, and supplies, making them the most widely used basic mechanical components. They are characterized by a large variety of types and specifications, diverse performance and applications, and a high degree of standardization, serialization, and generalization. 

It typically includes the following 12 categories of parts:

1. Bolts: A type of fastener consisting of a head and a threaded shank (a cylinder with external threads), used in conjunction with a nut to fasten two parts with through holes. 1. **Bolt Connection:** This type of connection is called a bolted connection. Since the two parts can be separated by unscrewing the nut from the bolt, a bolted connection is a detachable connection.

2. Studs: A type of fastener without a head, consisting only of threads at both ends. When connecting, one end must be screwed into a part with an internally threaded hole, and the other end passes through a part with a through hole. Then, a nut is screwed on, thus securing the two parts together as a single unit. This type of connection is called a stud connection, and it is also a detachable connection. It is mainly used when one of the connected parts is thick, a compact structure is required, or frequent disassembly makes bolted connections unsuitable.

3. Screws: Also a type of fastener consisting of a head and a shank. According to their use, they can be divided into three categories: machine screws, set screws, and special-purpose screws. Machine screws are primarily used for fastening a part with a set screw threaded hole to a part with a through hole, without requiring a nut (this type of connection is called a screw connection, which is also a detachable connection; it can also be used with a nut for fastening two parts with through holes). Set screws are mainly used to fix the relative position between two parts. Special purpose screws include eye bolts for lifting parts.

4. Nuts: Nuts have an internal threaded hole and are generally shaped like a flat hexagonal prism, but can also be flat square or flat cylindrical. They are used with bolts, studs, or machine screws to fasten two parts together, making them a single unit.

5. Self-tapping screws: Similar to machine screws, but the threads on the screw are special self-tapping screw threads. Used to fasten two thin metal components together as a single unit. Small holes need to be pre-drilled in the components. Due to their high hardness, these screws can be directly screwed into the holes, creating corresponding internal threads.

6. Wood Screws: Similar to machine screws, but with special wood screw threads. They can be directly screwed into wooden components (or parts) to fasten a metal (or non-metal) part with a through hole to a wooden component. This type of connection is also detachable.

7. Washers:Fasteners shaped like flat, round rings. Placed between the supporting surface of bolts, screws, or nuts and the surface of the connected parts, they increase the contact surface area of ​​the connected parts, reduce the pressure per unit area, and protect the surfaces of the connected parts from damage. Another type of elastic washer also prevents the nut from loosening.

8. Retaining Rings: Installed in the shaft grooves or shaft hole grooves of machines and equipment to prevent parts on the shaft or in the hole from moving laterally. 9. Pins: Primarily used for positioning parts, and sometimes for connecting, fixing, transmitting power, or locking fasteners.

9. Rivets: A type of fastener consisting of a head and a shank, used to fasten two perforated parts (or components) together as a single unit. This type of connection is called a riveted connection, or simply riveting. It is a non-detachable link because separating the two connected parts requires breaking the rivets.

10. Components and Connecting Pairs: Assemblies are fasteners supplied as a set, such as a combination of a machine screw (or bolt, self-tapping screw) and a flat washer (or spring washer, locking washer); connecting pairs are fasteners supplied as a set of specialized bolts, nuts, and washers, such as high-strength large hexagonal head bolt connecting pairs for steel structures.

11. Welded Studs: A type of fastener consisting of a shank and a head (or no head), used to fix other components to a part (or component) by welding, so that it can be connected to other parts.