Arbor Mount Flap Disc, 4-1/2", 40, Coarse/ HOLE DIAMETER: 0.875 INCHES NOMINAL SCREEN GRIT SIZE DESIGNATOR: 40 USAGE DESIGN: METALWORKING MAXIMUM SPEED RATING IN RPM: 13300.0 WHEEL DIAMETER: 4.500 INCHES NOMINAL SPECIAL FEATURES: CLOTH BACKING; FLAT STYLE, 20-25 DEGREE ANGLE; ABRASIVE MATERIAL:ZIRCONIA