Tiger® Depressed Center Grinding Wheel, Performance Line, 9 in Wheel Diameter, 1/4 in Wheel Thickness, Quick-Change Connector, 24 Grit, Coarse Grade, Premium Aluminum Oxide Abrasive, Wheel Type Number: Type 28, 6600 rpm Maximum, Resin Bond, Applicable Materials: Carbon Steel, Structural Steel, Cast Iron and General Purpose Metals, 5/8-11 Center Hole Thread Size, Wheel Hardness: R, Yes Reinforced, Specifications Met: ANSI B7.1-2010