I'm not terribly knowledgeable about guns, and my curiosity has gotten the better of me. What's the purpose of an adapter like this?
It's a cleaning tool, to allow you to capture once used cleaning solvent.
It can also be used to attach a silencer made from an oil filter; provided you fill out the proper paperwork beforehand. You'd need to read up on NFA laws. Ridiculous, but that's how it is... This is still just a thread adapter, either way. It merely facilitates the attachment of an oil filter. Use it as a solvent trap, or make a suppressor out of it... The choice is yours, just know your laws and regulations before doing it. The primary intent is to recycle cleaning fluids. An oil filer does this with no modifications. It you modify it to be a suppressor, that's on you to register it. I know I'm being redundant, but I want you to understand, the thread adapter is nothing but a thread adapter, no matter what you choose to do.
A brief synopsis: gun haters require guns to be loud so they can use noise ordinances to restrict ranges. Silencers (properly known as suppressors) are, in reality, an essential piece of safety equipment. Not the 'bad guy' tool that lying politicians make them out to be. Imagine how hard it is to instruct new gun owners while we're all wearing earmuffs... Its stupid. Irritating your neighbors if you practice. The law has a very devious ulterior motive, like most laws... Imagine if it were against the law to put a muffler on your car... That's how absurd this is. But it is what it is...
I have a new design in the works for a much better filter that has never been used in this market before. It will do more than just catch used solvents and lube, it will clean them up. This isn't just some excuse to make silencers out of oil filters. There is a real need for recycling your maintenance fluids in the current political and fiscal climate.