Z-Solid Has High Concentration Of Zirconia Grain As Well As Heat Treated Aluminum Oxide Grain. Z-Solid Grain Will Achieve Twice The Cutting Action Of Other Premium Ao Discs. Zirconia Grain Is Sharper And The Grain Breaks Down Over A Longer Period Of Time And Thus Far Superior Results Can Be Achieved Compared To Ao Grains. Z-Solid Provides High Metal Removal And Is Excellent On Stainless Steel, Inconel, Titanium And Tool Steel.