Fastener is a kind of mechanical part which is widely used for fastening connection. Fasteners are widely used in various industries, including energy, electronics, electrical appliances, machinery, chemical industry, metallurgy, mold, hydraulic industry, etc. various fasteners can be seen in various machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, chemicals, instruments and supplies, which are the most widely used mechanical foundation parts. 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 call the fastener of a kind of national standard as standard fastener, or simply as standard fastener.