There are usually two types of transmission mechanisms in the transmission chain: one is the transmission mechanism with fixed transmission ratio and transmission direction, such as fixed ratio gear pair, worm and turbine pair, which is called fixed ratio transmission mechanism; The other is the transmission mechanism that can change the transmission ratio and transmission direction according to the processing requirements, such as the change gear transmission mechanism, sliding gear transmission mechanism, etc., which is called the displacement mechanism.

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.