| FEPA grains Micrometer (µm) min. - max. |
Grit size designation Diamond & CBN |
| 212 - 250 µm | D 251 / BN 251 |
| 180 - 212 µm | D 213 / BN 213 |
| 150 - 180 µm | D 181 / BN 181 |
| 125 - 150 µm | D 151 / BN 151 |
| 106 - 125 µm | D 126 / BN 126 |
| 90 - 106 µm | D 107 / BN 107 |
| 75 - 90 µm | D 91 / BN 91 |
| 63 - 75 µm | D 76 / BN 76 |
| 53 - 63 µm | D 64 / BN 64 |
| 45 - 53 µm | D 54 / BN 54 |
| 38 - 45 µm | D 46 / BN 46 |
Grinding tools with diamond are marked green (D) and grinding tools with CBN are marked red (BN).
For grain sizes D46/BN46 and larger, all manufacturers adhere to the FEPA (Federation of European Producers of Abrasives) standard. The largest grain size in micrometers (1/1000 mm) + 1 gives the grain designation. A D126 means that the abrasive grains are up to 125 µm or 0.125 mm in size.
The higher the number of the grit size designation, the larger the diamond or CBN grain. In the case of mesh size designations used for conventional ceramic wheels with silicon carbide or corundum, it is exactly the opposite. Here, the designation corresponds to the number of mesh in a sieve of one inch length, through which the grains can still be sieved through. A D126 corresponds approximately to 120-140 US mesh and the finer D46 to 325-400 US mesh.
| Micro grains Micrometer (µm) min. - max. |
Grit size designation Diamond & CBN |
| 30 - 40 µm | D 41 / BN 41 |
| 32 - 38 µm | D 39 / BN 39 |
| 22 - 36 µm | D 37 / BN 37 |
| 25 - 32 µm | D 33 / BN 33 |
| 20 - 30 µm | D 31 / BN 31 |
| 15 - 25 µm | D 26 / BN 26 |
| 12 - 22 µm | D 23 / BN 23 |
| 10 - 20 µm | D 21 / BN 21 |
| 8 - 15 µm | D 16 / BN 16 |
| 6 - 12 µm | D 13 / BN 13 |
| 6 - 10 µm | D 11 / BN 11 |
| 4 - 8 µm | D 9 / BN 9 |
| 3 - 6 µm | D 7 |
| 1 - 5 µm | D 6 |
| 2 - 4 µm | D 5 |
| 0.5 - 3 µm | D 4 |
| 1 - 2 µm | D 3 |
| 0 - 1 µm | D 2 |
Unfortunately, the various manufacturers of diamond and CBN grinding tools do not use uniform grit size designations for micro grains. Everybody does it differently. To make an example, a grit size with 20 to 30 micrometer large diamonds is designated by one manufacturer as a D25 and by another as a MD20. We, however, designate it as a D31, since we use the logic in the larger grain designations also for the micro grains:
Largest grain in micrometer +1 = HAEFELI designation.
Everything else is just confusing; it is always the largest grain that makes the largest groove in the workpiece and decisively influences the surface quality.
Exception: For historical reasons we have used the designations D30 and BN30 which do not follow this system as they are not based on the largest grain. Beginning in 2018, we will successsively replace them with the systematically correct designations.
If you want to print out a grain size table, it would be best to print out the relevant page in the catalogue.
Haefeli Diamantwerkzeugfabrik AG
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CH-8046 Zürich
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