They're NOT the same!
This particular page is intended to help you determine which type your bike is equipped with, because there is a great deal of confusion about which is which.
The terms «freewheel» and «cassette» are often used interchangeably, an error that causes a lot of wasted time and money.
Freewheels for Threaded Hubs
Traditional rear hubs came with a standardized set of threads to which a standard freewheel/sprocket cluster could be screwed on. This allowed any brand of freewheel to be mounted on any brand of hub. If you wore out your sprockets, or wanted different gear ratios, you could unscrew the cluster and install a new one.
Almost all bikes made through the late 1980s used this system.
Over the last few years the Shimano «Freehub» has largely replaced the conventional threaded rear hub. It is sad to lose the brand interchangeability that formerly existed, but these hubs work so well that they have come to represent the new «standard.»
From left to right: Traditional Threaded Freewheel; Traditional Threaded Hub; Cassette Freehub; Cassette Cluster
The cassette Freehub incorporates the ratchet mechanism into the hub body (although the ratchet mechanism is still replaceable). When you wear out the sprockets on a Freehub, you replace the sprockets only, not the ratchet mechanism (which typically lasts much longer than the sprockets).
The sprockets are commonly sold as a set, called a «cassette». The sprockets in a cassette are usually held together by three small bolts or rivets for ease of installation. These bolts or rivets are by no means necessary, they just make it easier to keep the sprockets and spacers in the correct order and position when they are removed from the ratchet body. Individual sprockets are also available.
Identification: Freewheel or Cassette?
- Commonly 5−, 6- or 7−speeds
- Extractor splines do not turn when sprockets are spun backwards
- Commonly 7−, 8−, 9- or 10−speeds
- Lockring splines turn with sprockets when spun backwards
- Many cassette Freehubs have a distinctive bulge on the right end of the hub barrel.
Shimano Hyperglide Freewheel,
Shimano Cassette Freehub,
Shimano Cassette Freehub, showing characteristic bulge on the right side of the body.
Not all Freehubs have this bulge, but whenever you see it, you can be sure that it is, in fact, a cassette Freehub.