The whole device. When a centrifugal clutch is mounted on a minibike, it is common to install it so the sprocket is facing the engine, and Comet makes one that will install either way.
There's a pic on this minibike forum that shows what I mean. It is using a jackshaft, but ignore that part. Notice how the clutch is installed so the sprocket is facing the engine:
http://www.oldminibikes.com/forum/ge...lutch-tav.html