If you use it, you have broken the law if you have not paid the stamp.
That goes for any Suppressor you build w/o following the rules and paying the stamp.
If your caught w/ the adapter, a threaded gun and a filter, you MAY be up for prosecution.
You are allowed to build your own suppressor AFTER you pay the stamp, thus parts to build your own suppressor are out there. Just like parts for you to legally build your own firearm are out there. You just have to follow the laws (ie, don't brake the laws)
Thanks for the info. I'm just curious. Hard to imagine anybody would actually use one of the things. Or maybe, "Here, hold my beer while I screw this Fram filter onto my gun."