On a
bicycle, the
cogset or cluster is the set of multiple
sprockets that attaches to the hub on the rear
wheel. A cogset works with a rear
derailleur to provide multiple
gear ratios to the rider. Cogsets come in two varieties,
freewheels or
cassettes, of which cassettes are a newer development. Although cassettes and freewheels perform the same function and look almost the same when installed, they have important mechanical differences and are not interchangeable.