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What Grit is a Norton Fine, Medium and Coarse?

Norton makes a number of stones in a Fine, Medium and Coarse grit. But those grits are seldom stated in terms of the actual grit. Based on our experience and referencing their documentation, we have determined the grits. Interestingly, Norton produces different grits for their Norton India Stones (an aluminum oxide stone) and their Norton Crystolon Stones (a silicon carbide stone).

While there is no one standard in use for grits, we generally use the standard most commonly associated with waterstones (JIS). Why do we do this? For a few reason actually. First, on the lower grits, it fairly closely follows the USA standard (CAMI) for coated abrasives (sandpaper) and the European standard (FEPA). Second, the waterstone standard has a very wide range that starts very coarse and finishing extremely fine. The CAMI and FEPA standards stop where the waterstone grits keep going finer. This allows us to use one standard across different stones. Lastly, the micron measurement allows for excellent on relative particle size comparison, so from that perspective, that is a great way to measure grit. However, if you're not familiar with that measurement, the numbers are somewhat hard to interpret. For example, a 45 micron particle size is hard to imagine, but if we said it was roughly a 325 grit, you gain some perspective.

Norton India and Norton Crystolon Grit Chart

Stone Type Coarse Grit Medium Grit Fine Stones
Norton India Stone 150 240 400
Norton Cystolon Stone 120 180 320