I have to disagree with this. The thumb should not be loose. If the thumb hole is too loose it cause you to squeeze the ball tighter throughout you swing. The best article I have found on the subject is one written by Ron Clifton which can be read here ...
http://www.bowl4fun.com/ron/btm04_files/btm4.htm
If you read the 4th section of ball fit and weight it specifically talks about thumb fitment ... The care and feeding of a thumbhole
If you keep reading the 5th section talks about how tight the thumbhole should be ... How tight should the thumbhole be? The very first sentence says it all ... "In my opinion, the thumbhole should be tight enough that you don’t have to squeeze the ball during the swing but not so tight that you have to really force your thumb into the ball."
It is a very good read so I hope it helps you.
Bookmarks