A sprocket[1] or sprocket-wheel[2] is a profiled wheel with the teeth, or cogs,[3][4] that mesh with a chain, monitor 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 gear in that sprockets should never be meshed together directly, and differs from a pulley in that sprockets have teeth and pulleys are simple.
Sprockets are used in bicycles, motorcycles, cars, tracked automobiles, and other machinery either to transmit rotary motion between two shafts where gears are unsuitable or to impart linear movement to a monitor, tape etc. Probably the most typical form of sprocket may be found in the bicycle, where the pedal shaft carries a huge 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 driven by sprocket and chain system, a practice generally copied from bicycles.
Sprockets are of various designs, a maximum of efficiency becoming claimed for each by its originator. Sprockets typically don’t have a flange. Some sprockets used with timing belts possess 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 being used rather than belts or ropes and sprocket-wheels instead of pulleys. They could be run at high speed and some kinds 
of chain are so built concerning be noiseless actually at high speed.