cassette

Cassettes are a modern bicycle part that are a key component of the recumbent tricycle drivetrain.

A cassette has cogs of increasing size with inner splines that engage the opposing splines of a freehub body. The freehub is attached to the hub or is part of the entire hub construction.

Cassettes and freehubs are the successor to the freewheel which dominated the bicycle industry for decades. Freewheels interface to the hub by screwing onto threads incorporated into the hub.