When is a grit not a grit?
Scales for measuring grit size are arbitrary, and different ones exist. What's important is the actual size of the cutting particles in microns. The Norton combo uses a 6μ/3μ grit, which makes it coarser than the the equivalent Shapton 4K (3.68μ) and 8K (1.84μ) stones. The Norton 4K side is closer in coarseness to the Shapton 2K (7.35μ), and the 8K side is approximately equal to a Shapton 5K (2.94μ)
So two stones can be labeled as having the same grit, yet have different cutting abilities.
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