These premium grinding wheels are designed to resist glazing and grind cooler on all types of steel, and they are perfect for grinding high speed steel. Hard, sharp particles of aluminum oxide grit are held in a vitreous bond which breaks down easily in use, constantly exposing fresh, sharp grit to the edge being ground. Any tool can be ground faster and cooler, with considerably less risk of overheating and drawing the tool's temper. Wheels are provided with bushings for 5/8" and 1/2" arbors. Maximum safe speed is 4200 rpm for 6" wheels, 3200 rpm for 8" wheels. Wheel code is 38AJ5V.