Perfect for small edges and pointed tools; this 4" continuous surface stone works big in tight spots. 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).