Fasteners are a kind of mechanical parts which are used for fastening and connecting. Fasteners, industry widely used, including energy, electronics, electrical appliances, machinery, chemical industry, metallurgy, mold, hydraulic, and so on, in all kinds of machinery, equipment, vehicles, ships, railways, Bridges, buildings, structures, tools, instruments, chemical industry, instrument and apparatus, such as the above, you can see all kinds of fasteners, is the most widely used mechanical components. It is characterized by a wide variety of specifications, performance and use of different, and the degree of standardization, serialization, generalization is also extremely high. Therefore, some people have a national standard of fasteners called standard fasteners, or referred to as standard parts.