A better question is why thread them? Brownells Hi Force Solder will hold them just fine, as long as you have them closely fitted and pre tinned. The one time I threaded barrel stubs it was a real nightmare. You have to be sure that your monoblock ends are perfectly perpendicular to the bores and the the shoulders on the barrels are the same way. Then the barrels must be threaded perfectly and the monoblock the same. Lastly you have to put them in very tightly and get the surfaces down flush with each other. I found it very hard to thread and solder the stubs in because everything has to be really hot to allow you to get them tightly down where they belong. It is much easier to get them tightly together by soldering. Threading weakens the monoblock walls substancially and I don't see that it does that much good above the soldering. Bob