I've fitted a new shower mixer. As I couldn't find one with the exact spacing for the original pipes, I went for one which has a pair of cranked couplers on it, so you can adjust the spacing between hot and cold inlets by up to 3 cm.
You screw on the couplers into the existing female threads in the wall, adjust to correct spacing and then connect up the shower mixer which has female threads.
The problem lies in the coupling attachment to the wall. It's screwed in, but not fully tight. If it was then it wouldn't be adjusted correctly and the mixer wouldn't fit.
I'm worried that with a power shower it will leak. What's the answer here - is there some kind of cement I can use?