According to the letter of the law, they CAN charge you with illegal possession of an NFA item for owning an oil filter.
"Oh but they'd never do that, that's ridiculous!"
It is ridiculous. UNLESS you happen to have either of the following:
1. An adapter that fits the oil filter threads on one end and firearm barrel threads on the other end.
2. A firearm with a barrel that has been specially modified with threads that match oil filter threads.
Do you have a firearm with a threaded barrel, and an oil filter?
Don H is correct.
Oil filter threads don't match any of the standard threads used on firearm barrels. You would have to possess an adapter or have had one of your firearm barrels threaded with non-standard threads that match an oil filter before the ATF could gain any traction for a prosecution.