These 4 In. x 3/16 In. thick center wheels feature 24 grit surface with a 5/8 In. arbor hole. Depressed center grinding wheel for metal polishing and general flat grinding. Aluminum oxide abrasive grains are evenly distributed to give a smooth surface. Tool must be properly guarded. 4 In. x 3/16 In. x 5/8 In., 24 grit, maximum safe speed 13,690 RPM, 5 pack. Use for model 9523NB, 9526PBH, N9514B, N9501BZ and 9523NBH.