For those who prefer a continuous diamond surface; especially for sharpening small or pointed tools; these bench stones outperform them all. Extra FineDMT 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.Extra-Fine - Refines knife or tool edge to razor sharp perfection.Colour code: Green. Diamond size: 9 micron (1200 mesh).