Never changed one, as its originally riveted I can see why it was only sold as a complete assembly, as to differences I really don't know, possibly a different number of teeth for a different primary ratio. Might be worth asking on the US site if anybody knows what the difference is also try emailing Western Hills Honda as they have found obsolete stock for me in the past. If you have time try trawling motogrid site to see if any of the associated parts like chains and bearings altered plus if you go to your local dealer with the numbers the old price list used to tell you if a part had been superseded.
