Make a recessed o-ring in place. This liquid silicone hardens to a perfect consistancy. Just find a yo-yo with a groove, squeeze this stuff in, and unlike other silicones, it will flow to become perfectly smooth and level (remember to let it dry overnight in a place where it will flow flat). No smoothing needed. This will work in any yo-yo with a groove, like yo-yojams, or modded yo-yos. 50g tube.