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 materials.[5][6] The name ‘sprocket’ applies generally to any wheel upon which radial projections sprockets engage a chain passing over it. It is distinguished from a gear in that sprockets should never be meshed together straight, and differs from a pulley in that sprockets have teeth and pulleys are easy.
Sprockets are found 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 motion to a track, tape etc. Maybe the most common form of sprocket could be found in the bicycle, in which the pedal shaft carries a large sprocket-wheel, which drives a chain, which, subsequently, drives a little sprocket on the axle of the trunk wheel. Early automobiles were also largely powered by sprocket and chain system, a practice largely copied from bicycles.
Sprockets are of various designs, a maximum of efficiency getting claimed for each by the originator. Sprockets typically don’t have a flange. Some sprockets used with timing belts possess flanges to keep the timing belt centered. Sprockets and chains are also used for power transmission in one shaft to another where slippage is not admissible, sprocket chains being used rather than belts or ropes and sprocket-wheels instead of pulleys. They may be operate at high speed and some types of chain are so built as to be noiseless actually at high speed.
