Merit Flexible Mini Grind-O-Flex Abrasive Flap Wheel, Round Shank, Aluminum Oxide, 3" Dia., 1" Face Width, Grit 120, 20000 Max RPM (Pack of 10) Aluminum oxide is durable and the most common abrasive grain Cloth backing is stiffer, tougher, and thicker than a paper or film backing Flap wheels conform better to the workpiece than a disc, and are commonly used for grinding and finishing on irregularly shaped workpieces Round shank for use on a wide variety of toolholding systems Flexible to produce smooth, even finishes on parts with complex geometries