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 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 should never be meshed together directly, and differs from a pulley for the reason that sprockets have tooth and pulleys are easy.
Sprockets are found in bicycles, motorcycles, vehicles, tracked vehicles, and other machinery either to transmit rotary movement between two shafts where gears are unsuitable or to impart linear motion to a track, tape etc. Probably the most common form of sprocket could be within the bicycle, in which the pedal shaft bears a huge sprocket-wheel, which drives a chain, which, in turn, drives a little sprocket on the axle of the rear wheel. Early automobiles had been also largely powered by sprocket and chain mechanism, a practice generally copied from bicycles.
Sprockets are of various designs, no more than efficiency becoming claimed for each by the originator. Sprockets typically do not 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 isn’t admissible, sprocket chains becoming used rather than belts or ropes and sprocket-wheels instead of pulleys. They may be operate at high speed plus some forms of chain are so built concerning be noiseless also at high speed.