A
freehub is a type of
bicycle hub that incorporates a
ratcheting mechanism, and the name
freehub is a registered trademark of
Shimano. A set of
sprockets (called a "
cassette") are mounted onto a
splined shaft of the freehub to engage the
chain. The ratcheting mechanism is a part of the hub, in contrast to a freewheel, an older technology, which contains both the sprockets and a ratcheting mechanism in a single unit separate from the hub. In many high-end and midrange bicycles, freehubs have replaced freewheel systems.