> Something doesn't sound right, but I don't have the 3M mask, so I can't
> give you an accurate answer.

> Shawn

Yeah. the cartridges that I have won't open up (easily) to accept the prefilter. the cartridges have one installed on the inside when purchased but there were extras that came in the bag. I am going to go to West and see what the replacement cartridges look like maybe you can't split the ones that i own.

Tom