I was chatting with Nick last night...complaining about the blisters on my thumb. He offered some help but because I'm clueless I couldn't give him my hand measurements. I keep getting blisters on the sides of my thumb, most on the same side but I already added side pitch and I still rub so I'm not sure. Nick said I probably needed to oval my thumb, have any of you guys done this and has it helped any? I plan on adding some forward pitch to with maybe some reverse on the fingers, need to get this grip problem fixed.
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-If you're not willing to change, you're not willing to improve.

-Life is like a coin, you can spend it any way you want, but you can only spend it once.

-I will forever love this great game, I love the people and the competition, I only wish the best would get the recognition of an ATHLETE that they deserve.

I oval all my thumb holes myself.
I bought a drum sander attachment for a standard hand drill. They come in 3/4 to 1 inch. Price around $10 - 12. Advantage is you can take material out slowly.
With fingers in place thumb in top of hole mark where both sides of the thumb touch. Then oval by sanding both sides. You get a custom fit that a pro shop may not want to spend the time doing.
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A Born again bowler with a mission to bowl 300.