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 material.[5][6] The name ‘sprocket’ applies generally to any wheel where sprockets radial projections engage a chain passing over it. It really is distinguished from a equipment in that sprockets are never meshed together directly, and differs from a pulley in that sprockets have the teeth and pulleys are soft.
Sprockets are found in bicycles, motorcycles, vehicles, tracked automobiles, 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 could be found in the bicycle, in which the pedal shaft carries a big sprocket-wheel, which drives a chain, which, in turn, drives a little sprocket on the axle of the rear wheel. Early automobiles had been also largely driven by sprocket and 
chain mechanism, a practice generally copied from bicycles.
Sprockets are of varied designs, a maximum of efficiency becoming claimed for each by its originator. Sprockets typically don’t have a flange. Some sprockets used in mixture with timing belts have flanges to keep the timing belt centered. Sprockets and chains are also used for power transmission from one shaft to another where slippage is not admissible, sprocket chains getting used rather than belts or ropes and sprocket-wheels instead of pulleys. They could be operate at high speed plus some forms of chain are so constructed as to be noiseless even at high speed.