When a bowler buys a ball, the first logic step is to get it drilled so they can throw it.
The problem is, drilling a ball is somewhat of a permanent thing, unless you want to pay $40-$50 to have the hole plugged and redrilled, but too many times being redrilled can also affect the ball performance.
This being said, the chosen size of the finger and thumb holes is something that you are going to have to deal with for the lifetime of the ball.
One thing that bowlers will find out, however, is that there are many factors that can cause the feel of the ball to change, even from day to day and in some cases, game to game.
When it is colder outside, your fingers are going to shrink some, and even a slight shrinkage is going to make the ball feel completely different on your hand.
If you have bowled too many games, you may even get some swelling in your fingers, also making the ball feel different. Finally, weight loss can affect the way a ball feels too.
Whatever the reason, you are most definitely going to experience changes in finger and thumb size once in a while. The best cure for this, even though it is scary to some to attempt themselves, is to put bowling tape in the holes.
I have personally had nights where I have put tape in after one game and then removed it for the final game, in order to keep the feel consistent.
There are many types of tape and many sizes to choose from, so it is important to know what each will do.
For most people, tape is inserted to tighten the hole up, and this can be done with smooth black tape.
If you also feel like you need a little grip in the hole as well, there is white tape with a gritty texture to it, and this will give you that extra hold.
Sometimes, bowlers need to get out of the ball easier, and there is even a slick white tape that can be inserted that will help your thumb slide out quicker.
Regardless of your need, there are things you can do to keep a consistent feel. There is obviously an art to inserting this tape as well, so if you are considering trying some tape, just ask your local proshop worker, or a veteran bowler for some help. They will be happy to walk you through the process.