I typically use black 1 3/8 Vise thumb slugs, but have been experimenting with the IT system as I am particular about my bevel and prefer a rougher feel.
My span and thumb hinge indicated a need for 5/16 reverse pitch which was what my pro shop operators drilled for years. I got a job in the pro shop as a teenager and did some experimentation on my own.
Like you I found that no matter how tight I made the hole, I still squeezed the crap out of the ball.
I just drilled up a piece for myself one day as a gag at 1/4 forward just to see what would happen. I was pleasantly surprised with what I had done.
I backed off a little on it to only an 1/8 forward in the thumb, but I definitely have a more secure grip now. I should add that this was probably a major benefit to me seeing as how I have a relatively short thumb and moist skin. I use a lot of rosin on my thumb like Wes Malott too.
My spans are 4 3/4 and 4 7/8 full so the traditional methods would be up in arms. I don't see it as a detriment at all.
I should make a note though. I find that the size of the hole becomes a little more critical, or at least for me it does. I have to go a little bit bigger than before and add two pieces of tape in my ball. I find in game 1 both pieces work, gm 2. I take one piece out, and gm 3 all the tape comes out. If you get the thumb too tight, it may be difficult to get that good, clean release we're all striving for.
I hope this helps
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