Type 27 Raised Hub. Made for a wide range of grinding, shaping and cutting jobs in home workshops, farms and machine shops. Aluminum oxide is recommended for all types of ferrous metals. Wheel dimensions are diameter x thickness x arbor. Wheel Thickness (in.): 1/4, Wheel Type: Metal grinding wheel, Wheels (qty.): 1, Wheel Diameter (in.): 4 1/2, Max. RPM: 12,000, Arbor Size (in.): 7/8