Crankshaft pulleys

Pulley — frictional wheel with rim or groove on circle which transfers the movement to drive belt or rope. It is used as one of the main parts of the belt gear, there are also pulleys on cam-shafts of mechanical blocks.
Unlike the block, the pulley transfers effort from axis to belt (or from belt on axis); the block rotates on axis freely and provides only change of the direction of the movement of belt or rope.