You need a twist on model with 2 set screws. Put it on and tighten it as much as possible. Shoot 30 rounds through it, (or heat it up with a torch), and re-tighten it with the included Allen wrench by hand. With it as tight as possible when hot, let it cool down, and it will automatically indent the barrel. Once it is cool, tighten it until you can't turn it any further, and shoot 20 more rounds from it. Turn it as tight as possible while hot, and let it cool down. Once it is cooled, tighten it again. It will set into the barrel even further. Let it cool for 24 hours. It will now be securly mounted. I did this for my aftermarket SKS recoil suppressor from CTD, and the only way I can get it off now is if I get a hammer and chisel to pound it off with the set screws removed. It absolutley will not come off by hand, no matter how hard I try. I actually have it on so tight that I really don't even need to put on the lock nuts. When pushed all the way down, I hear an audible *click* because the flash supressor shrunk by 3/1000th's of an inch in diameter to make it absolutly tight against the barrel. With the set screws all the way in, it will never come off.