I tried putting a jammin buggy spur gear (50 tooth i believe) on the mutilator diff cup and the diff cup is a hair too big. I don't know of a smaller spur that would fit on the mutilator diff housing. I called ofna a while back and they said the jammin cr and crt spurs will not fit. I'm probably going to just dremel the chassis a bit and rig some sort of spacers for the top so I can use the top diff plate to clear the spur.