John
If you bowl enough, you are going to build up callouses. It is from friction and releasing the ball properly will result in callouses. There are correct callouses and callouses built up from blistering.
As far as proper fit, in regards to pitch, you have to start with a proper fit. If your fit is wrong, then pitch is a band aid.
After making sure your span is correct, then pitch is used so that the bowler does not have to grip or squeeze the ball to hold onto, as well as releasing at the proper place in the swing or approach.
You can tell by when you start placing your thumb into the thumb hole, if the thumb is forced into an unnatural angle. As well as any hindurance at the release. The hand should not be forced in an unnatural position to release the ball due to pitch.
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Formerly BrunsRico
As posted by Steven..."None other than our esteemed JustRico!!"