Walter Surface Technologies Depressed Center Wheel, High Performance, 4-1/2 in Wheel Diameter, 1/4 in Wheel, Thread Connector, 24 Grit, Extra Coarse Grade, Aluminum Oxide Abrasive, Wheel Type Number: Type 27, 13300 rpm Maximum, Resinoid Bond, Applicable Materials: Cast Iron and Steel, 5/8-11 Center Hole Thread, Black Wheel, Specifications Met: ANSI B7.1, EN 12413