4-1/2" x 1/8" x 7/8" Arbor, Masonry Depressed Center 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, Bulk.