Sprocket

A sprocket or sprocket-wheel is a profiled wheel with teeth or cogs that mesh with a chain, track or other perforated or indented material. The name "sprocket" applies generally to any wheel upon which are radial projections that engage a chain passing over it. It is distinguished from a gear in that sprockets are never meshed together directly, and differs from a pulley in that sprockets have teeth and pulleys are smooth. The word "sprockets" may also be used to refer to the teeth on the wheel.