Interchangeable Inserts

Dec 19th 2022

Why do some bowlers have interchangeable and others do not? 

Interchangeable thumbs have become a very common part of today’s competitive bowling environment.  Non-Competitive Bowlers, that drill several bowling balls a year, find it very beneficial as well.  

Interchangeable Inserts have been around for over a decade.  As I have been going through old bowling magazines, I have found a couple examples of adjustable pieces for inside your bowling ball.  
Ball Thumb Control for inside your bowling ball.

Pro Grip Adjust a Grip Bowling Ball Insert


What are the benefits?  The largest benefit that comes to mind, is the ability to change sizes in a matter of seconds.  With a standard thumb hole, you would have to sand open a hole by going into the pro shop and having them work it out.  Sometimes there is a cost.  If you are at a tournament, there might not be anyone available to make an adjustment.  Some bowlers find that they swell or shrink often.  In the 80s/90s a company called Vise Grip/Exactacator made an adjustable thumb slug, that had a special key to loosen and tighten a piece inside the thumb hole.

Exactactor Bowling Ball Adjustable Thumb Slug

This thumb never caught on with pro shops. I have only seen one in my years in the industry.  Before today’s internet age, spreading information in the 90’s was mainly done by an instruction manual or bowling ball seminiars.  How many people have sat down and read an instruction manual?

I am a bowler that has 5 to 10 pieces of tape in a thumb hole.  Some bowlers don’t like using more than 1 piece of tape.  With an interchangeable thumb, you can easily drill a smaller or larger thumb to switch out when needed.

When traveling for tournaments, a lot of bowlers will experience swelling due to air travel/cabin pressure.  Once on a trip to Reno, I went to start practice and my thumb wouldn’t fit in a bowling ball.  This instantly put me into a panic because I didn’t know if there was anyone that had tools to open up my thumb hole.  I wasted most of the practice time working out each ball.  The next day, my thumb was back to normal, and my thumb holes were now enormous.  I spent a lot of my mental energy worrying about my thumb hole, and the release of my thumb hole. This type of situation could have been easily fixed with an interchangeable thumb hole.

There are two disadvantages to interchangeable thumb holes.  

The first is the low occurrence that they break.  The failure rate has greatly decreased since they have come into the market place. Please be sure to keep pieces out of extreme hot and cold situations.  But that is the same for your bowling equipment.

The second issue that we have encountered are pro shops not being able to drill to the correct depth.  Each interchangeable thumb system comes with a specialized drill bit.  On that bit is a stopper, so that every thumb depth is the exact same. Some pro shop do not have their drill presses set up to allow the bit to drill down to the stopper. This is not an issue if you continue to go to the same pro shop, but if you need a thumb slug made by another pro shop (example - traveling) then you could have a problem.

Overall, if you are having problems with shrinking or swelling, talk to your local pro shop to see if this would be a good option for you. There are several interchangeable thumb systems on the market, but your pro shop should be familiar with most of them, and will let you know if any of them are right for your game.