Pulley is a type of wheel used for belt drives, usually made of cast iron, steel sheet, or aluminum. Its role is through the belt and its contact, through friction power will be transmitted to other parts, transfer rotational power and torque. It's keep the belt tight, reduce the possibility of relaxation and slip, so as to ensure the normal work of the engine. In addition, pulley can reduce noise and vibration, extend the life of the belt and other parts.