Grinding wheel, metal type 27, depressed center, 4″ x 1/4″ x 5/8″ arbor a24r. aluminum oxide metal Grinding wheel. designed for metal grinding, metal abrasion, body work, metal fabrication and general repair work. used on ferrous materials. for use on right angle grinders. wheel size: 4″ thickness: 1/4″ arbor: 5/8″ spec: a24r max rpm: 13,700 tool type: right angle grinder