This kit features the updated style of vise bases for the larger line of GRS vises, one rubber and one plastic. The rubber base provides more surface friction, allowing the vise to stay stabilized and limits the amount of movement and tilt. The plastic base is a smoother, harder surface that is great for when you want to tilt and move the vise more freely within the base. These bases fit GRS Standard Block (003-530, 003-531), Low-Profile Vise (003-615), Satellite Vise (003-784), MagnaBlock (003-021, 003-52), and Positioning Vise (003-541).