Mike, it has been my experiance, you cannot dismiss a consumable as not being military use based on the lack of a NSN. As John can attest, there are many parts on the shelf at 202 for the AHSVS project that do not have a NSN on them. Some of these were bulk and therefore the only NSN was on the larger case, other times they were a LOP item and no NSN on the box.
However, without knowing the size or any other details of this filter, it is pretty much impossible to identify it. I appears to me to be either a fuel or oil cartridge.
Length, diameter, etc would be required to narrow it down. Even at that it may not be of military use at all.