shower arm elbow plate issue

[ahearsum]

I'm installing a shower head elbow wall plate (for the first time). The depth of the 1/2 inch threaded socket isn't enough to clear the depth of the backer board (see attached picture) plus a further 12mm of tile and adhesive. The joint between the shower arm and the elbow would be right in the middle of the wall. Call me old fashioned but this makes me nervous. I thought there would be various depths of elbow available but I can't find them . I see there are extensions (pictured below) but that has the same issue of a screwed joint in the middle of the wall and in many ways might be worse if I ever needed to change the arm (what would prevent the extension from slightly loosening and possibly leaking?).
Any thoughts/guidance appreciated.

 

[oldbuffer]

1. File flats either side of the cylindrical extension piece so that you can put a spanner on it. Stop it turning while fitting / removing shower arm.
2. Fit the extension to the back plate elbow with Loctite 577 or Flomasta Pipe Seal.
3. Fit the shower arm to the extension with Loctite 55. Should give a good seal but easier to undo than the 577 / Flomasta join.
4. If you have to cut the extension piece down, you can do it with a hacksaw, then file the end flat and square to the cylinder. Insert a "sacrificial" 1/2" BSP threaded piece while cutting / filing, then turn that out to clean the cut threads.

 

[ahearsum]

Thanks oldbuffer for such a prompt reply and such practical suggestions. I had thought about trying to solder the extension on to the elbow. Would that work with a tight screwed joint?
I will use one of your suggestions but is it a bit odd that deeper elbows don't exist?

 

[Stivino]

I'm assuming you're going to fit a bar shower onto those fittings? If that is the case, will you not need a male thread like this?

 

[Stivino]

I had thought about trying to solder the extension on to the elbow.

That works, I've done it. I cut the ends off two old bath taps to use as extensions keeping the good, machined ends to the outside.

 

[ahearsum]

I'm assuming you're going to fit a bar shower onto those fittings? If that is the case, will you not need a male thread like this?

Thanks but it's a male threaded bar as in the picture

 

[ahearsum]

BTW this drawing hopefully makes things clearer