# How do you control what angle plumbing joints go in at?

I'm an electrical engineer, working on repairing a somewhat complicated pneumatic system, but I figured this would probably be the best place to ask. This is probably a very basic question to anyone who works in plumbing, but I couldn't find anything about it online.

When you have right-angle pipe fittings, the kind with NPT threads that you screw together, how do you control what angle they screw in to? If you just screw two things together, the relative angle between them will be essentially random as it depends on the exact angle of where the thread starts and how far the threads engage. But we need to put in pipe at specific angles to align fittings to other parts of the system, so how does one actually do that?

• I had this question myself - I think the crux of your question is, how tight does a fitting need to be, and can I still adjust the angle at that tightness? Maybe this will help- diy.stackexchange.com/questions/12670/… – Aww_Geez Mar 31 at 13:56
• I don't understand the question. Tapered threads (any steel threads, really) self-align as you begin assembly. You'll find that there's a lot of rigidity in the components once they're even loosely assembled. – isherwood Mar 31 at 13:59
• @isherwood If that's the case, then there is no way to control the angle a right-angle fitting will be pointing when it bottoms out. I think the OP assumes the fitting needs to be bottomed out, and would like clarity on that. – Aww_Geez Mar 31 at 14:01
• @isherwood I'm talking about rotational angle. Imagine using two 90° fittings to offset a pipe by a little bit--how do you ensure that the pipes on both ends are parallel to each other? – Hearth Mar 31 at 14:01
• Consider making an edit to add a picture of the area in question. – Ecnerwal Mar 31 at 20:31