A sprocket assembly comprises a first sprocket (54) which serves as a hub for a larger second sprocket. An annular extension member (70) is secured to the outer periphery of first sprocket (54) to prevent relative axial movement. The annular extension (70) comprises teeth (77,81) on both an inner edge (76) and an outer edge (80). The inner set of teeth (77) may be rounded so as to mate and lock with the profile of teeth of the first sprocket (54). The outer set of teeth (81) provide the larger second sprocket and engage with a chain (56).
