Are you talking about the removable slugs. I have them in two balls for about a month. It feels nice having each ball feeling exactly the same.
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Bowl To Win!!!

I've seen several of these used all over the place. It is a great idea for pro shops and all, but I, personally, think its just another way for pro shops to make your bowling equipment costs more expensive. It really isn't all that hard for me to do my own thumb, close my eyes, and not be able to tell the difference between the feel of my thumbholes. It's going a little to far, IMO.

It is a good concept, but I do not think it is practical enough for me to get.
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-Jeremy Vitug

This system in theroy of course works quite well.  But in practical use it is very expensive to install for most bowlers. plus there is the issue of now static weights are changed because you must use a 1 1/2 drill bit for the outter sleeve. but this design is much better than the others i have i seen.
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Timothy @Juniors Pro-Shop
Montreal, Quebec.