Yes, it works best with two bearings. Most (all?) Duncan yo-yo's have the same size bearing as the BK. The second bearing fits very, very snug. The way I get mine in there is to use a nut, bolt, and a washer to squeeze the bearing in there. Order from the tip side: bolt, washer, rip cord, bearing, nut smaller than outer diameter of bearing.
It can be tough to get the fixed tip out. You need a hole, or a pipe to hold the Rip Cord point down while you whack at it with some sort of blunt nail and hammer. It is likely the o-ring will be ruined when you take it out, so there may be challenges to making it fixed tip again, should the need arise.
