I used a dremal. It will chuck right up into the colar. And it went ok....a week later it was binding again. Another local used a ball cup reamer and has report ball cup perfection. He used a 4mm one from tunigy, but some members cut a couple groves in old studs, popped them into the cup and ran it low speed. This is my next plan of attack. Sanding was "ok" and better than stock, but still lacking IMO. I have a bigger type local race this weekend and need to go through 3 cars. If I have time I will try the ball cup reamer method. Maybe even borrow one for that local racer.