60 grit FEPA-F (250 micron) Should be used with water, soapy water or oil Compatible with Edge Pro and Hapstone Custom made by Gritomatic Working surface 152 x 25 x 6 mm (6" x 1" x 0.25"), mounted on aluminum blank Boride Sharpening Stones are used for sharpening knives on Edge Pro and Hapstone Pro knife sharpeners. Boride offers a wide range of stones with different performance values and different rates of wear. Boride stones are made of aluminum oxide. All Boride stones are 6 mm thick and are mounted on high quality aluminum blanks. Stones that are 6 mm thick offer a longer life cycle than stock Edge Pro stones that are 3 mm thick and are becoming a community standard. RUBY series stones are made of aluminum oxide and are high performance stones designed for roughing work. They are available only in coarse grain. RUBY series is in great demand for coarse sharpening.