Weiler 51204 Tiger X Flap Disc, Ceramic and Zirconia Alumina, Angled, Phenolic Backing, 36 Grit, 4-1/2", 5/8"-11 UNC Nut (Pack of 10) Industry-First X3 Technology combines an advanced grain anchoring system, dual flap design and engineered backing that delivers faster grinding AND longer disc life for increase productivity Triple Split Coat anchor grains securely to maximize grinding at moderate pressure Dual flap design pairs Ceramic Alumina and Zirconia Alumina grain to grind faster and last longer Engineered poly cotton fiber backing wears consistently to maximize the life of the Ceramic Alumina and Zirconia Alumina grains