Weiler Big Cat High Density Abrasive Flap Disc, Type 27, Round Hole, Phenolic Backing, Zirconia Alumina, 4-1/2" Dia., 120 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 keeps disc from scratching the workpiece and offers durability and reinforcement High-density abrasive and larger flaps for prolonged life over standard flap discs Unthreaded round hole for attachment to grinding tools