Flap disc, blue zirconia, 40 grit type 29, depressed center, 4-1/2″ with 7/8″ arbor za40, for right angle grinders. cuts fast and outlast sanding discs 10-to-1. great flexibility. ideal for rough or fine finishing. multiple layers of zirconia cloth flaps constantly exposing new extra sharp grinding points. laminated by state-of-the-art automated equipment. reinforced fiberglass backing plate. each disc balance tested for vibration-free grinding/finishing. wheel size: 4-1/2″ arbor: 7/8″ grit: 40 spec: za40 max rpm: 13,500 tool type: right angle grinder