We want to make sure that you get the correct adapter. Please verify that you want 1/2-28 female to 1/2-20 male. This will take a firearm that is threaded 1/2-28 and convert it to 1/2-20 for use with 1/2-20 suppressors and accessories. Most USA suppressors and accessories are 1/2-28 so if you have a firearm that is threaded 1/2-20 and you want to convert it to 1/2-28, then you do not want this adapter. You would instead us part # 00243. If you have a suppressor that is 1/2-20 and you want to use it on a firearm that is threaded 1/2-28, then this is the adapter that you want.