4-1/2" x 1/4" x 7/8" Arbor, 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 13,300.