A
sprocket or
sprocket-wheel is a profiled
wheel with teeth, cogs, or even sprockets that mesh with a
chain,
track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections 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.