Superior Pads and Abrasives PP40 4" Semi flexible rubber backing pad with Velcro for Stone Sanding. This backing pad is used with different diamond grit polishing pads. Wet diamond polishing pads are used with wet polishers or wet grinders. It is flexible and can polish either contoured surface like Ogee, Full Bull nose, Half Bull nose, Bevel, Demi or flat surface. It is recommended to always use with water at rpm 2200 for best results. RPM may vary depending on stones and its hardness with a 4500 max RPM.