Orientating a pressure gauge
Imagine, if you will, that your whole plumbing system was threaded pipe. Which was common in many places for a certain time period...

With pipe fittings, you don't get a choice of orientation on threads. You just work with them as they come, and there is some practical leeway between "so loose it leaks" and "too tight" which is how you get things to align - proper use of decent pipe dope helps with this.

So, solder it in any which way. Tighten until the gauge faces the way you want, without leaks.

If you are super-fussy and like overly complex and expensive solutions, you can insert a union between the gauge and the rest of the system. 

There are other options, such as using a compression fitting where the threads and the seal are separate functions, and the fitting does not turn as the nut is tightened. You could think of those as "fittings that act like a union."