You've seen those advertisements on social media such as Facebook from Wish and other sellers selling items that look suspiciously like mostly-finished unregistered suppressors.
Because, well, they are.
In the words of Admiral Akbar:
And verily, it is.
Possession of suppressor parts or a bunch of parts that can be quickly manufactured into a working suppressor by a quick drilling when you don't have the accompanying approved Form 1 or Form 4 along with your $200 tax stamp is rather bad news and really not advised.
That's because you may get a personal visit from people bearing bad news for you, or you may just get a letter like this as a new client of mine just did:
It seems that Diversified Machine Co, an online seller of such "solvent traps", was allegedly selling solvent trap kits that could be turned into a fully working suppressor a little too readily for the BATFE's tastes.
In short, if you are acquiring a solvent trap or fuel filter that looks suspiciously like a suppressor save for a little extra hole, and you don't Pay $200, then Do Not Pass Go.
Otherwise, you may Go Directly To Jail.