"VACU inserts allow for swelling and shrinkage of the fingers. VACU inserts are installed in an 1-1/32"" hole instead of 31/32"". VISE insert is inserted into VACU sleeve, glued, and then the whole assembly is glued into the ball. Use VISE inserts 1.5-3 sizes smaller than normal for VACU inserts. Since the insert is smaller than normal, it will expand in the larger hole. When your fingers swell, so does the insert. When your fingers shrink, so does the insert. You will be able to increase your ball speed & rev rate with VACU inserts. Also, since the inserts hold on to you instead of you squeezing the ball, you will ""free-up"" your armswing. Price for 1 insert and 1 sleeve. You choose the insert."