Weiler Big Cat High Density Abrasive Flap Disc, Type 27, Threaded Hole, Phenolic Backing, Zirconia Alumina, 4-1/2" Dia., 60 Grit (Pack of 1) Zirconia alumina abrasive is self-sharpening and more durable than aluminum oxide Type 27 depressed center flap style is used for weld blending, deburring, deflashing, edge chamfering, stock removal, and grinding and finishing in one step Phenolic backing for durability and reinforcement of the disc High-density abrasive and larger flaps for prolonged life over standard flap discs Threaded hole for attachment to grinding tools