The knivesandtools.com website rates them as similar to a Japanese 3000, 6000 and 8000 grain size.
But what will they be in terms of microns?
Based on Grand Unified Grit Chart, my guess is 4.5, 2 and 1.2 Micron, but I’m no expert…
I used these new optical image values in revision 9 of my grit chart. The original 1500 was apparently at least as fine as the 3000 stone, which agrees with the 5 micron value I had for it before. See the thread Organic linked above.