A sprocket[1] or sprocket-wheel[2] is a 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 where radial projections engage a chain passing over it. It is distinguished from a gear in that sprockets are never meshed together straight, and differs from a pulley for the reason that sprockets have tooth and pulleys are smooth.
Sprockets are found in bicycles, motorcycles, cars, tracked automobiles, and other machinery either to transmit rotary motion between two shafts where gears are chain sprocket unsuitable or even to impart linear movement to a track, tape etc. Maybe the most typical form of sprocket could be found in the bicycle, where the pedal shaft carries a sizable sprocket-wheel, which drives a chain, which, in turn, drives a little sprocket on the axle of the trunk wheel. Early automobiles were also largely driven by sprocket and chain system, a practice largely copied from bicycles.
Sprockets are of various designs, no more than efficiency being claimed for each by its originator. Sprockets typically do not have a flange. Some sprockets used with timing belts possess flanges to keep the timing belt centered. Sprockets and chains are also utilized for power transmission in one shaft to another where slippage isn’t 
admissible, sprocket chains being used rather than belts or ropes and sprocket-wheels instead of pulleys. They can be run at high speed and some kinds of chain are so constructed as to be noiseless actually at high speed.