FlexOvit HP Depressed Center Grinding Wheel, Fast Grind, 4-1/2 in Wheel Diameter, 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