Zirconia alumina is self-sharpening and durable, allowing for a faster cut rate than aluminum oxide * Type 27 depressed center wheels are used for cutting off and portable grinding * Reinforced design helps provide safety, strength, and straight cuts * Resin bonds soften under the heat of grinding, releasing dulled abrasive grains * Depressed center wheels for use on right angle grinders, also called angle grinders, without gouging the workpiece