I would like to offer one more good point about using epoxy. Tonight i drill a ball that was rather tight at the bottom of the thumb hole and the insert would bind and leave about 2" exposed in the dry fitting. The epoxy also acts as a lubricate when pushing the insert into the thumb hole. After I put the epoxy in the thumb I was able to push the thumb insert all the way to flush. If you currently don't use epoxy I strongly suggest you give it a try. The only draw back is the bowler has to wait 1 hour before using the ball but the thumb insert sets up in about 5 minutes.
Thanks
Mike
Use super glue, tap it in with a hammer and don't let it sit at one spot very long. -- JohnP