According to the structure, it can be divided into roller chain, toothed chain and other types, of which roller chain is the most widely used. The structure of the roller chain is shown in Figure 1, which is composed of the inner chain plate 1, the outer chain plate 2, the pin shaft 3, the sleeve 4 and the roller 5. The inner chain plate and the sleeve, the outer chain plate and the pin shaft are respectively connected by interference fit, called the inner and outer chain links; The gap between roller and sleeve, sleeve and pin is fit. When the inner and outer chain plates are relatively bent, the sleeve can rotate freely around the pin shaft.

The chain is generally a metal link or ring, which is mostly used for mechanical transmission and traction. Chains used to block the passage of traffic (such as in the street, at the entrance of a river or harbor), and chains used for mechanical transmission.