Featuring the signature polka-dot pattern innovated by DMT¬; Diamond Whetstone» sharpeners are often imitated in appearance; but never equalled in quality or performance. The interrupted surface of tiny wells trap metal debris to ensure clean; continuous edge contact while the superior diamond does its work. For the quickest; cleanest sharpening; there truly is no substitute. Comes in a Plastic Case. CoarseDMT uses micronized monocrystalline diamonds bonded to a substrate in giving a consistent grit size and coverage across the stone, this process ensures a long lasting performance. Rather than going up in numbers for the finer stones, they refer to the size of the diamonds in Microns.Coarse - Quickly restores a dull edge to cutting sharp. Colour code: Blue. Diamond size: 45 micron (325 mesh).