The 3M™ Depressed Centre Wheel is a Type 27 grinding wheel that containing grade 24, aluminum oxide mineral. This coarse grade product is good for general metalworking and relatively high stock removal.Complete solutions. Its what youve come to expect from 3M, the leading supplier for metalworking industries. For over 100 years, 3M has been a proven leader, providing advanced technology and innovative solutions for increased productivity, enhanced efficiency and improved manufacturing processes.