Check the listing for details. Turbo Thumb Switch Grip Inners Blank (Choose Color). Condition: New. Listed at 13.97 USD. The Switch Grip Blank Inner Sleeve fits into the Outer Sleeve. With the new Blank Sleeve you are now able to insert a custom thumb mold into it and use as a normal Switch Grip. Get the same great feel in every ball with Switch Grip Interchangeable Inserts. This revolutionary two-piece insert assembly allows bowlers to remove and interchange thumb inserts from one ball to another for the same fit and feel every shot. No more fussing and fighting installing and removing tape. With just a simple "Twist & Click", bowlers can make a ball change using the same thumb or better yet change thumb size due to shrinking or swelling. This is the thumb insert piece and you will only need one of these unless you are drilling different sizes for shrinking or swelling. The inner diameter of the Blank Inner Sleeve is 1 1/4".