FlexOvit® HP™ Depressed Center Grinding Wheel, Fast Grind, 4-1/2 in Wheel dia, 1/4 in Wheel Thickness, Arbor Connector, A30S Grit, Super Fine Grade, Aluminum Oxide Abrasive, Wheel Type Number: Type 27, 13300 rpm Maximum, Resin Bond, Applicable Materials: Metal and Stainless Steel, 5/8-11 Center Hole Thread Size, Wheel Hardness: S, Specifications Met: ANSI B7.1. FlexOvit® HP™ A1236H Fast Grind Depressed Center Grinding Wheel, 4-1/2 in dia x 1/4 in Thick, A30S Grit, Aluminum Oxide Abrasive