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 where radial projections engage a chain moving over it. It really is distinguished from a equipment 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 used in bicycles, motorcycles, vehicles, tracked automobiles, and other machinery either to transmit rotary movement between two shafts where gears are unsuitable or to impart linear motion to a track, tape etc. Maybe the most common form of sprocket may be found in the bicycle, where the pedal shaft bears a large sprocket-wheel, which drives a chain, which, subsequently, drives a little sprocket on the axle of the rear wheel. Early automobiles had been also largely powered 
by sprocket and chain mechanism, a practice generally copied from bicycles.
Sprockets are of various designs, no more than efficiency getting claimed for each by the originator. Sprockets typically do not have a flange. Some sprockets used in combination with timing belts have flanges to keep the timing belt centered. Sprockets and chains are also utilized for power transmission from one shaft to some other where slippage isn’t admissible, sprocket chains becoming used rather than belts or ropes and sprocket-wheels instead of pulleys. They can be operate at high speed and some kinds of chain are so constructed as to be noiseless actually at high speed.