Re: considering a suppressor
Ok bad information here. DO NOT use a 5.56/ 223 suppressor especially non serviceable ones in a 22lr! 22lr are VERY dirty if you put those rounds through a sealed 5.56 can your going to gunk it up.
If you want to buy a suppressor the best bang for your buck to start with is a USER SERVICEABLE ( take apart ) 22lr can. Do the research there is a difference between brands you want to get the one that does the best at what it does.
I own a outback ii mine has been jailbroke ( made user serviceable ) but it is a great suppressor though there are better choices. The more you plan on using it the more you need to clean it.
The "oil filter" thing is a bad idea for legal reasons.
A suppressor IS a firearm according to the ATF so you buy one you get the tax stamp and you can put it on any firearm you wish to. The only exception is if you want to avoid a two stamp SBR you can permanently attach the suppressor the the short barrel making it the legal 16" or more and then it woudl not be a SBR however then you woudl be unable to move the suppressor between weapons.
You can use a suppressor on any smaller caliber as long as it is within specks for pressure. Again do NOT use any sealed large caliber suppressor on a 22lr.
As for threads 22lr and 5.56 both use 1/2x28 as the standard. The issue is with LENGTH! Most 22lr threads are .400 the AR threads are .600. If your 22lr is threaded to long you will erode the blast baffle. These a GENERAL sizes the suppressor you buy will tell you what size ( remember thread size includes LENGTH ) you need to make it work best.
Also another note on caliber swapping. Suppressors have there bore cut to the caliber they are designed to work with. Using a suppressor with a larger then needed through hole will decrease the effectiveness of it.