Weiler Tiger Abrasive Flap Disc, Type 29, Round Hole, Aluminum Backing, Zirconia Alumina, 4" Dia., 36 Grit (Pack of 1) Zirconia alumina abrasive is self-sharpening and more durable than aluminum oxide Type 29 angled style is more aggressive than type 27 style and is used for weld blending, deburring, deflashing, edge chamfering, stock removal, and grinding and finishing in one step Aluminum backing for rigid support Designed for use at a 15- to 35-degree angle Unthreaded round hole for attachment to grinding tools