CGW 42315 Flap Discs | Z3 Premium Zirconia. Fastest grain removal in the marketplace for carbon based steels. Recommended for aggressive use and heavy duty applications. Active grinding agent provides cool cutting with light pressure. Special optimized resin bond offers maximum cutting capacity, strong edge stability and long life. Premium Zirconia Alumina grain with a poly/cottonheat treated backing. The poly/cotton combination provides low stretch and strength for the high Zirconia concentration of Z3. Available in Regular Thickness and XL Thickness.