"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. Max. RPM 12,000, Wheel Diameter in. 4 1/2, Arbor Size in. 7/8, Wheels qty. 1, Wheel Thickness in. 1/4."