Hi Mutt,
Grit sizes are ususally determined by the actual grit size of the abrasive particle used to make the abrasive. There are various meshes that are used to screen the particles to ensure consistent sizes.
In the case of ceramic abrasive, the actual particle is a man made sapphire called "alumina". The particle size is actually 15 microns. The grit created is the result of different firing processes and final processing in the case of the ultra fines.
We've never found a way to grit them, many experts have "guessed" as to what they are closest to, but I've seen expert "guesses" all over the field.
So we call them medium, fine and ultra fine.
Our diamonds are 600 mesh.
I wouldn't use oil on the medium as it is open celled and will absorb the oil like a regular whetstone. I've spoken with some that have used oil on the fine and ultra fine. I guess it's a manner of preference.
We recommend to use them dry as it cuts faster and is cleaner.
sal
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