I've got a few of them in tbe drawer but I don't think they're the micro brakes. I think I have some that are 1/2-32 tpi and also some that are 9/16-32 tpi. The od is about .800 so I dont think you could turn it all the way down to .650 but you surely could cut a taper on it to blend it into the barrel. Let me know if these might work for you.