Depressed Center Wheels, Abrasive Wheel Type Type 27, Abrasive Wheel Diameter 4 1/2 in, Thickness 0.25 in, Arbor Hole Size 5/8 In.-11, Abrasive Material Ceramic, Abrasive Grit 20, Max. RPM 13,580 RPM, Series Quantum 3, Grade Extra Coarse