Holes or indentations for gripping purposes shall not exceed five and shall be limited to one for each finger and one for the thumb, all for the same hand.  The player is not required to use all finger holes in any specific delivery, but they must be able to demonstrate, with the same hand, that each gripping hole can be simultaneously used for gripping purposes. Any thumb hole that is not used for gripping purposes during the delivery would be classified as a balance hole.

all it says is there has to be something in the thumb hole to concider it a gripping hole ,  no where in this rule does it state it has to be your thumb.. I designed a  bowling glove with a nub in the palm that fits perfectly in the thumb hole  now 1" deep for gripping purposes there for IM still able to have a weight hole in my ball because the NUB is now gripping the thumb hole by the way there rule states...  USBC didnt like my fix but agreed with me today when I talked to them and he said as long as its in the ball its concidered a gripping hole then i said so IM still able to have a weight hole in any ball, he said that would be correct.. ..  figure that 1 out...   LMAO