GatorGrit, 9" x 1/4" x 5/8"-11 Arbor, Hubbed Metal Depressed Center Grinding Wheel, Double Reinforced With Industrial Grit & Glue For Increased Life & Durability, Superior Friability Allows Wheel To Break Down Quickly, Consistently Exposing New Grain For Increased Sharpness & Longer Life, For Low Angle & Vertical Grinding, Max RPM Rating 6,600.