For those who prefer a continuous diamond surface; especially for sharpening small or pointed tools; these bench stones outperform them all. Extra Extra 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.Extra-Extra Coarse – Recommended for extreme stock removal to repair a much damaged edge or to quickly change a bevel angle. This grit is a safe alternative to power grinding, cutting quickly without heat build-up that can ruin tool temper. Colour code: Silver. Diamond size: 120 micron (120 mesh).