Clay bar grits?!

[Supergus1]

For years I've been using Meguiar's clay bars with great results, however recently after my shift at a large auto parts warehouse, I went to the front store to get a clay bar. Apparently Meguiars doesn't sell just the clay bar:dunno:. The counter person said that we carried Clay Magic brand. Then he asked if I wanted the fine or the medium grit?! I never knew there was a difference. So how on earth do I really know what I need and more importantly, how do I know what I'm getting?

[oldmodman]

Blue is fine. Red is medium or aggressive. At least within the Clay Magic brand.

And I remember reading that Ricardo's is the mildest. But I don't think it is sold in the USA

[WRXINXS]

What is the finest grade of clay available on Autogeek? Pinnacle or Sonus or something else?