Diamond paste and spray are graded directly in microns by the industry (Kemet, Engis, and others). Maker figures (hollow), no distribution published, so each is a point.
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.
Particle sizemicrons, log
1003010310.30.1
coarserfiner
inkmeasured or standardmaker figureour estimate
shapeknown distributionpoint, spread unknown
90 micronMaker-published
90 µm
Coarsest common paste grade (Kemet, Eternal Tools).