It's in the link at the top of the page, but caterpillar uses 2micron absolute. That's 97% guaranteed. It's a mighty large filter, though and it's slowwwwwww. Anyway, just because particles will pass through a system does not mean they won't damage it. I think someone used the sandpaper analogy earlier... Maybe another thread. Anyway, the point is any abrasive material will do some extent of damage.