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 sprockets generally to any wheel where radial projections engage a chain passing 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 vehicles, 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. Probably the most typical form of sprocket may be within the bicycle, where the pedal shaft carries a huge sprocket-wheel, which drives a chain, which, subsequently, drives a little sprocket on the axle of the trunk wheel. Early automobiles had been also largely powered by sprocket and chain mechanism, a practice mainly copied from bicycles.
Sprockets are of various designs, a maximum of efficiency getting claimed for every 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 utilized 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 instead of pulleys. They may be run at high speed plus some types of chain are so built as to be noiseless also at high speed.