FEPA-B grades CBN (cubic boron nitride) grain.ISO 6106 uses one sieve table for both diamond and CBN, so the B bands equal the D bands. The B-number is the largest grain in microns plus one, not a median, a convention worth knowing when a wheel cites it.
Each grade below shows its size in microns, its spread (the published distribution, where a maker or standard gives one; most makers publish none), and where that size lands on the reference scale, a shared yardstick for reading grit numbers across makers.