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.

All parts of the chain are made of carbon steel or alloy steel and heat treated to improve strength, wear resistance and impact resistance. Roller chains can be made into single-row chains and multi-row chains. When transmitting large power, double-row chains or multi-row chains can be used. The bearing capacity of multi-row chain is proportional to the number of rows. However, due to the influence of precision, the load borne by side-by-side chain is not easy to be uniform, so the number of rows should not be too large.