Fastener is a kind of mechanical part which is widely used for fastening connection. It is widely used in various machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, chemicals, instruments and supplies. It is the most widely used mechanical foundation. It is characterized by a wide variety of specifications, different performance uses, and standardization, seriation, generalization of the degree is also very high. Therefore, some people also call a kind of fastener with existing national standards as standard fastener, or referred to as standard fastener for short.