A sprocket[1] or sprocket-wheel[2] is a sprockets 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 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 tooth and pulleys are smooth.
Sprockets are used in bicycles, motorcycles, vehicles, tracked automobiles, and other machinery either to transmit rotary motion between two shafts where gears are unsuitable or to impart linear movement to a track, tape etc. Probably the most common form of sprocket could be within the bicycle, in which the pedal shaft carries a sizable sprocket-wheel, which drives a chain, which, subsequently, 
drives a small sprocket on the axle of the trunk wheel. Early automobiles were also largely powered by sprocket and chain mechanism, a practice generally copied from bicycles.
Sprockets are of varied designs, a maximum of efficiency being claimed for every by its originator. Sprockets typically do not have a flange. Some sprockets used with timing belts have flanges to keep the timing belt centered. Sprockets and chains are also used 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 rather than pulleys. They can be operate at high speed and some kinds of chain are so constructed as to be noiseless even at high speed.
