Pulleys

Pulleys are mechanical elements with the function of transmitting or guiding a movement to other mechanical elements. They are made of a central body, a hole for the linchpin, and the external part which has a cavity for a belt or a cable. Belts or cable, through friction, create motion and energy. In some cases, the external diameter can be smooth, flat or rounded. 

Pulleys can also just guide the movement: the cable runs on the external cavity of the pulley and this creates movement. 

Materials

Pulleys can be made of aluminium or plastic materials.