A flap wheel is comprised of a number of strips of abrasive material bound together into a wheel. Ours are "potted" wheels, bound together in a mold with epoxy resin to form a uniform, smooth and continuous running wheel. 4" and larger flapwheels come with a center hole (5/8" or 1" are standard sizes). Unmounted Flap Wheels   Sizes     Diameter: 4", 6", 8"     Width: 1/2", 3/4", 1", 1-1/2", 2", 3"   Material Specifications:     X-weight Aluminum Oxide Resin Bond Cloth     Other materials available on request   Grits Available:     320, 240, 180, 120, 80, 60, 40     Other grits available on request