Z3 Ultimate flap discs from CGW-Camel Grinding Wheels USA (www.cgwheels.com) are constructed of 100 percent zirconia alumina grain with a poly/cotton heat-treated backing. The material is sized between regular and extra large, and has less than 0.01 percent iron, sulfur and chlorine content. Discs are offered in 4 1/2-in. diameters, with grit sizes ranging from 36 to 80.