Zirconia alumina discs will last longer on general to heavy metal and woodworking applications. A&H Abrasives ? Psa Zirconia Alumina Sanding Discs Are Ideal For Wood Planing Or Heavy Grinding Of Ferrous And Non-Ferrous Metals: Rugged, Synthetic Zirconia Alumina Abrasive Is Blockier And Sharper That Aluminum Oxide. Micro-Crystalline Structure Allows For Controlled Breakdown And Self Sharpening. Resin Bonding On Heavy Duty Y-Weight Backing Can Be Used Wet Or Dry. Enhanced Pressure Sensitive Adhesive ( Psa ) Backing Adheres Solidly But Removes Easily When Worn. Made In USA With Components From Korea And USA.