Square: It's basically a short, non-hex pipe nipple. Brass, joining two things I don't want damaged. Heat not an option as there's an O-ring/piston on one of the components. Decided to just say f*ck it. Found out there's a Swagelok nearby, so I'm going to go there tomorrow and get a hex nipple for $5 that has perfect threads and some of their dope in lieu of tape.