Depressed Center Wheels, Abrasive Wheel Type Type 27, Abrasive Wheel Diameter 4 in, Thickness 0.25 in, Arbor Hole Size 5/8 in, Abrasive Material Aluminum Oxide, Abrasive Grit 24, Max. RPM 15,200 RPM, Series High Performance, Grade Very Coarse, Application Ferrous Metal