No problem, I also picked up quite a few M1 filters on clearance at Wal-Mart. The way I read the count, the M1-455a cartridge filter is an average filter for capturing particles in the 21 micron range.I know absolutely nothing about this but would love to hear some analysis. Very curious. Especially since I have a Pentastar and about 12 M1 filters that I picked up on clearance at Wallyworld.
What does it tell us? Thanks for posting, OP, btw!