Vise Insert Ball ItThis is the piece that is mounted to the bowling ball.The Vise Inserts Ball-It and Ball Expander are used in conjunction with a Vise IT slug. These two pieces are mounted inside the thumb hole of your bowling ball. The Ball-It is used to hold your IT thumb slug in place inside the thumb hole.The Ball-IT fits all three size of Vise IT thumb slugs – 1 1/8″, 1 1/4″, 1 3/8″