A sprocket has a hub with a screw thread, i.e. the sprocket is screwed onto the hub body. A cassette is mounted on a freewheel body that is screwed onto the hub and fixed by means of a lock ring. From a mechanical point of view, the two systems are completely different and not compatible. Many sprocket combinations with different numbers of teeth are available for cassettes. The bolt-on sprockets are slowly dying out and the number of gradations is limited. Cassettes are the way forward.