Find the lowest prices on bike cassettes from Shimano, Campagnolo, SRAM and more! Did you know - freewheels and cassette freehubs, they are not the same! These two terms "freewheel" and "cassette" seem to be used interchangeably, but let's be clear about the differences. Traditional rear hubs came with a standardized set of threads, and you would attach a freewheel / sprocket cluster by screwing it on. This design permitted any brand of freewheel to be mounted on theoretically all hub brands. In the past, when the sprockets wore out, or different gear ratios were desired, you could unscrew the gear cluster and install a new one. Most every bike produced up until the late 1980's worked this way. Now let's talk about cassette freehub. The Shimano "freehub" has pretty much replaced the conventional threaded rear hub design. It was nice benefit over bike cassettes to be able to interchange gears so easily, but cassettes certainly do have their advantages. The improved cassette design has been used for bike parts on most bicycles since the late 1980's until now. The cassette freehub uses a ratchet mechanism in the hub body. It attaches to the rear hub, and then separately, the bicycle cassette attaches to it. When the cassette sprockets on a freehub wear down, you replace the sprockets only - the ratchet mechanism which is the freehub stays in place. The sprockets, in turn, are collectively sold as a set, and are called a "cassette". Modern Hyperglide cassettes use a threaded lockring with which to secure the sprocket cluster to the splines of a freehub body. There is a special splined tool, that you use in conjunction with a chain whip, which fits the notched cutout of the lockring. The sprockets in a cassette are typically held together by three small bolts or rivets, which makes installation easy. Some more expensive bicycle cassettes use a spider - this is an intermediate metal casting to hold two, three or more largest sprockets in one piece. While this does cut down on overall cassette weight, the sprockets that are mounted on a spider cannot be interchanged to get different gear ratios. You have to treat the spider as a complete unit. Say you want to use a cassette from one brand - Shimano or SRAM - with the same number of sprockets or possibly fewer, but with a derailleur and shifter system from another brand's lineup. This can be done, though you might need to replace some of the spacers in order to get the correct spacing for the cassette. For some odd reason, you will find that 9-speed hubs and cassettes seem to operate fairly well with the opposite 9-speed brand.