recently like a month ago, my thumb decideds to grow like crazy, from calluses and stuff... almost everyday i have drill some space out or change my slug. its getting very FU*KING annoying and will it ever stop, or is it because recently i got serious into bowling about 7 months ago and now 30 games a week is catching me?
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EVERY PIN COUNTS!

http://www.jayhawkbowling.com/Pro_s_Corner/Fitting_Tips/fitting.html

Someone posted that for me in the Drilling section... worth reading through.  I have a similar problem as well, i think its because someteims my thumb swells.  But when i bowl, its not swolen, and it causes me to squeeze the ball a little bit to keep my thumb in the ball.  Or else it will flop around in the slug.

Humidity as well will cause swelling. Perhaps as the summer comes closer the temperature owling in your center is going up. I was bowling 100 games aweek for several months, now I am only bowling 8-10 a week. I have 2-3 extra peices of tape in the thumb hole of all my balls. So yes, the more you bowl the larger your thumb will get.
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Getting all the pins I can.