In the transmission device of machine tool, the commonly used transmission parts include pulley, gear, worm turbine, gear rack and screw nut, etc. Through these transmission parts, the power source and the actuator, or the two actuators are connected, which is called the transmission connection. A series of sequentially arranged transmission parts that constitute a transmission link are called transmission chains.

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.