A sprocket[1] or sprocket-wheel[2] is a profiled wheel with teeth, or cogs,[3][4] that mesh with a chain, track or other perforated or indented material.[5][6] The name ‘sprocket’ applies generally to any wheel upon which radial projections engage a chain moving over it. It really is distinguished from a gear in that sprockets are never meshed together directly, and differs from a pulley for the reason that sprockets have teeth and pulleys are even.

Sprockets are used in bicycles, motorcycles, vehicles, tracked vehicles, and other machinery either to transmit rotary motion between two shafts where gears are unsuitable or even to impart linear movement to a monitor, tape etc. Perhaps the most common form of sprocket may be found in the bicycle, in which the pedal shaft bears a large sprocket-wheel, which drives a chain, which, in turn, drives a small sprocket on the axle of the rear wheel. Early automobiles had been also largely driven by sprocket and chain mechanism, a practice largely copied from bicycles.

Sprockets are of varied designs, a maximum of efficiency being claimed for every by the originator. Sprockets typically do not have a flange. Some sprockets used with timing belts have flanges to keep the timing belt centered. Sprockets and chains are also used for power transmission from one shaft to some other where slippage is not admissible, sprocket chains being used rather than belts or ropes and sprocket-wheels rather than pulleys. They could be operate at high speed plus some types of chain are so built as to be noiseless also at high speed.