SHARPAL 116N 3 PC. Credit Card Size Diamond Sharpening Stone each measures L 3 1/4-inch x W 2 1/8-inch x D .14-inch. Fits easily in pocket or wallet. Each comes in convenient storage pouch. Industrial monocrystalline diamond is electroplated in nickel onto a steel base for longevity. Kit of 3: Coarse 325 grit (45 micron) to quickly restore a neglected edge; Fine 600 grit (25 micron) for a sharp edge; and Extra Fine 1200 grit (9 micron) to hone and refine a sharp edge after sharpening with a coarser diamond. Ideal for knives, small edged and pointed tools including carbide, high speed steel, titanium, ceramics and most any super hard material including the newer materials being used by most knife manufacturers. Sharpen dry. No messy oil needed. Patent pending ring grip holding protects hands from hurting when sharpen.