Ok here is how I determine if my thumb hole is correct. I prefer my thmb holes to be very snug. I will drill my thumb hole the normal 7/8's size. My pitch is 0-0. After the hole is drilled, I will take a bevelknife and bevel the front edge so that it is comfortable and does not grab. This is the area at the base of the thumb and webbing area. Then take the rotosander and smooth everything out. Once that is done I will place my hand in the ball and hold the ball down by my side. Close my eyes and feel for pressure anywhere on the surface of the thumb. Where there is pressure I will mark with a yellow or white pencil. after all the areas are marked I will take a piece of screen and work the opposite side of the whole from where the marks are. If the pressure is great I may take a bevelknife to the area until the pressure is gone. When the hole is prefect you will feel no pressure anywhere on the thumb at all. You are holding the ball without squeezing. The ball will not fall off but you are not grabbing either. It takes patience and practice to get it right. I will insert 1 piece of wide white tape and make sure everything is adjusted again and correct. The goal is to be able to hold the ball down by my side and feel no pressure anywhere on the grip.