Extra Coarse (Black) Fast: Real diamond, hardest material known, reduces sharpening time, Unique pattern speeds sharpening. Easy: Light pressure produces keen edge with few strokes. Clean: Non-porus surface resist laoding and wipes clean. Use only water for lubrication. Durable: Tough monocrystalline diamond resist wear. Versatile: Hones any hard material, steel, ceramic, glass, stone etc.