A sprocket[1] or sprocket-wheel[2] is a profiled wheel with the 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 where radial projections engage a chain moving over it. It is distinguished from a equipment in that sprockets are never meshed together directly, and differs from a pulley for the reason that 
sprockets have teeth and pulleys are clean.
Sprockets are used in bicycles, motorcycles, cars, tracked automobiles, and other machinery either to transmit rotary movement between two shafts where gears are unsuitable or to impart linear movement to a monitor, tape etc. Maybe the most typical form of sprocket may be within the bicycle, in which the pedal shaft carries a large sprocket-wheel, which drives a chain, which, in turn, drives a little sprocket on the axle of the rear wheel. Early automobiles were also largely powered by sprocket and chain mechanism, a practice mainly copied from bicycles.
Sprockets are of varied designs, no more than efficiency getting claimed for each by its originator. Sprockets typically don’t have a flange. Some sprockets used in combination with timing belts possess flanges to keep the timing belt centered. Sprockets and chains are also utilized for power transmission from one shaft to some other where slippage is not admissible, sprocket chains becoming used rather than belts or ropes and sprocket-wheels instead of pulleys. They may be run at high speed and some types of chain are so constructed as to be noiseless even at high speed.