A sprocket[1] or sprocket-wheel[2] is a profiled wheel with teeth, or cogs,[3][4] that mesh with a chain, monitor or other perforated or indented materials.[5][6] The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain moving over it. It is distinguished from a gear in that sprockets should never be meshed together directly, and differs from a pulley for the reason that sprockets have tooth and pulleys are soft.
Sprockets are found in bicycles, motorcycles, cars, 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 typical form of sprocket could be found in the bicycle, where the pedal shaft carries a large sprocket-wheel, which drives a chain, which, subsequently, drives a small sprocket on the axle of the rear wheel. Early automobiles had been also largely driven by sprocket and chain system, 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 combination with timing belts have flanges to keep carefully 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 getting used instead of belts or ropes and sprocket-wheels rather than pulleys. They could be operate at high speed plus some forms of chain are so built as to be noiseless also at high speed.