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PT When buying sharpening stones, especially professional tools like Aldim, you will notice that grit is measured in different units: Microns (μm), JIS (Japan), or FEPA (Europe).
Confusing these standards can lead to poor sharpening results—either leaving deep scratches or failing to achieve the desired polish. This guide will help you navigate the world of abrasives.
Why is Grit Measured Differently?
- Microns (μm): The most accurate way to measure grit. It refers to the actual size of the abrasive particles in thousandths of a millimeter. The smaller the micron number, the finer the stone.
- JIS (Japanese Industrial Standard): Common for water stones and many synthetic brands.
- FEPA (Federation of European Producers of Abrasives): Divided into FEPA-F (for bonded abrasives like Aldim) and FEPA-P (for sandpaper).
- TheUS Mesh standard refers to the number of openings per linear inch in a sizing screen. Higher Mesh Number = Finer Stone: A "400 Mesh" stone means the diamond particles passed through a screen with 400 openings per inch.
Ultimate Grit Conversion Table (Microns to JIS/FEPA)
This and another table shows how our Diamond and CBN Stones (measured in microns) compare to international standards:
| Abrasive Class | Micron Range (μm) | US Mesh (ASTM) | JIS (Japan) | FEPA-F (Europe) |
|---|---|---|---|---|
| Extra Coarse | 200/160 | 70 - 80 | #80 | F60 |
| Coarse | 100/80 | 140 - 170 | #180 | F120 |
| Medium | 40/28 | 325 - 400 | #400 | F280 |
| Fine | 20/14 | 600 - 800 | #1000 | F400 |
| Extra Fine | 7/5 | 1800 - 2500 | #3000 | F800 |
| Super Fine | 3/2 | 4000 - 8000 | #6000 | F1200 |
| Mirror Polish | 1/0 | 14000+ | #10000+ | Polishing |
Why We Use Microns
Unlike mass-market brands that use vague "grit" numbers, Aldim labels stones in microns (e.g., 20/14). This provides the highest level of precision for professional sharpeners.
- 20/14 means the particles are between 14 and 20 microns in size.
- This range ensures a consistent scratch pattern, which is vital for the structural integrity of the knife’s edge.
Pro Tip for Switching Between Brands
If you are moving from a #1000 JIS Water Stone to an Aldim Diamond or CBN Stone, you should look for the 20/14 or 14/10 micron range. Keep in mind that diamonds cut deeper than aluminum oxide, so a diamond stone of the same "grit" may feel slightly more aggressive initially.
- Instead of "Extra Coarse" (220 Mesh), choose Aldim 125/100 μm.
- Instead of "Fine" (600 Mesh), choose Aldim 20/14 μm.
- Instead of "Extra Fine" (1200 Mesh), choose Aldim 10/7 μm.