cassette

On a bicycle, the cassette is the stack of toothed sprockets on the rear hub. The chain moves across it when you change gear.

The number of sprockets is how modern gearing is counted, so an eleven-speed cassette has eleven of them, and the range between the smallest and largest determines how easily you can climb. It slides onto a splined freehub and is held with a lockring. Older bikes had a screw-on freewheel instead. The word also names the plastic tape cartridge that carried music before discs, which is where most people met it first.

Also practised as

• nounA plastic case holding magnetic tape.