I'm reassembling the gas line to my hot water heater. I'm at the last joint and I have the problem shown in Fig. 1.
I need to join A to B where A and B are both male and both fixed at the other end. So I'm considering using a coupler C. The problem is, no matter which way I rotate C, it's going to loosen at either A or B while tightening at the other. (And I need C to tighten at both A and B.)
How do I solve this problem and join A to B? Is there maybe a different fitting to use? Am I missing something, either obvious or not-so-obvious?Fig.1. Union of two male, fixed pieces of pipe
Edit: I just found this related answer over at engineering.SE.