Standard fasteners are divided into ten categories. The replacement should be determined according to the use occasion and function of the standard fasteners.
（1）The principle of selectivity
1.Considering the efficiency of processing and assembly, the variety of standard parts should be minimized in the same machine or project.
2.According to the expected use requirements of the standard parts, determine the alternative varieties in terms of type, mechanical properties, precision and thread.
1.Bolts: Bolts are generally matched with nuts (usually plus a washer or two washers), and are used for initial connection and fastening occasions.
2.Screw: The screw is usually used alone (sometimes with a washer), and it is generally used for fastening or tightening.
3. Studs: studs are generally two-way with threads (single-end studs are threaded at one end), usually one end of the rib is fastened into the body of the component, and the other end is matched with the nut to play the role of connection and fastening , But it also has the function of fixed distance in some.
4.Self-tapping screw: The screw hole of the workpiece matching with the self-tapping screw does not need to be tapped in advance. When the self-tapping screw is screwed in, the internal thread is formed.
When in use, the rod is inserted into the hole of the connected piece, and then the end of the rod is tightened for connection or fastening.
5.Pin: The pin is inserted into the workpiece when in use, and it usually plays a role of connection or positioning.
6.Retaining ring: The retaining ring is usually on the shaft or in the hole to limit the part.
7.Wood screws: Wood screws are used to screw into wood to connect or fasten.