Some do thread - others solder - soldering would be easier I'd think. I've always been better at soldering than threading. Get the parts 1 mil apart and solder - much easier.
Ron Vella went heat shrink as well as spot welding - more than one way to accomplish the same thing - attaching barrels to a monoblock.

Note, I've never done this - my opinion based on meager experience playing with guns'n stuff.