Buffing wheel ratings

[kmanuele]

Buffing and deburring wheels have ratings like 7P, 9P, 2S, etc., which doesn't seem to correspond to grit ratings.

For example, I see a 7P wheel with 180 grit, and a 7P wheel with 320 grit.

I think these relate to hardness, but wondering if someone can explain or decode them -- and how they would be used.

Thanks

Kevin