The 150mm (6in) W6 Diamond Whetstones are ideal for kitchen use and for the honing of smaller workshop tools. They have a large, wider diamond surface for sharpening a variety of knives and edges. Supplied in a plastic case fitted with non-skid rubber feet or wooden box, the base of the plastic case may be screw mounted to a bench. Black: Extra Coarse Grade 220, 60 micron.Blue: Coarse Grade 325, 45 micron.Red: Fine Grade 600, 25 micron.Green: Extra Fine Grade 1200, 9 micron. Ref: UTTK7433