Another nice upgrade but regarded by some as un-needed. Requires a 1/4" sprocket and turning the brake hub down to 1/4". In order to have an Oring drive chain, you need to go down to 520 chain. A 530 oring chain is too wide to work. It's nice not have to lube the chain so often. Works well, nice, but again, not really needed.
Some say the rear sprocket, which is also the brake hub, is vulnerable to wear witout machining. Making it thinner makes it even weaker. I like mine though. "Gold chain is perdy"