Insert Tape- The use of insert tape for the thumb hole I feel is very important. Having a good tight grip on the ball I feel is a must to a relaxed swing. Using white textured tape on the gripping side of the hole works best for me. It gives you something to hold onto without really having to grip tightly. The best fit would have your thumb exit the ball smoothly without hanging up or slipping off. If the ball feels like it is slipping, add a piece of tape. If you feel that it is a little snug, remove a piece. This is much easier and less costly than altering your grip unless you drill your own.