Wall mount tub filler rough-in & installation

[DanFL]

I'm installing this Kingston Brass wall mounted tub filler in my master bathroom renovation.
https://media.kingstonbrass.com/pdf/technical/install/kingston-brass-AE8157DL-install.pdf

Their instructions (step 4) assume that I will have access to the back side of the wall to connect standard flexible faucet supply hose. This is not the case (and as I understand, not code to bury the flex supply hose in the wall anyway). I was going to rough-in the hot/cold supplies with 2 standard 1/2" NPT brass drop elbows (right...?), and then use a brass nipple to make the final connection to the tub filler after the wall is finished. The nipples provided with the faucet are 1/2" NPS (straight thread, not tapered) on both ends. The female threads on the swing arm elbows (or dog legs, or whatever you call 'em) that connect to those nipples are also straight threaded. My research says NPS and NPT are not compatible and prone to leak.
So.. #1). What is the right way to do this? Can I use an NPT nipple on those straight female threads on the swing arm? #2). I'm also concerned about the "temporary" pressure test stub out from the drop elbow rough-in in the wall. I'd prefer to make that connection permanent since it's always under pressure (unlike a shower arm drop elbow which is past the shower valve) and not disturb that connection after the wall is finished since I would not be able to see if its leaking afterwards. Is it a bad idea to try to approximate the correct nipple size and only have to remove the cap after the wall is in? Any advice is appreciated.

 

[James Henry]

It's made for a free standing tub.

 

[Sponsor]

 

[DanFL]

Correct, I'm also installing a freestanding tub.

 

[James Henry]

Look at picture #2 on the drawing. if that's NPS then why does it say apply Teflon tape. just pointing it out, not interested in arguing.

 

[Terry]

Does the nipple allow soldering copper pipe inside?

 

[Terry]

Look at picture #2 on the drawing. if that's NPS then why does it say apply Teflon tape. just pointing it out, not interested in arguing.

But then HD has a video saying to wrap tape on faucet shanks and the faucets come with a tag on the shank saying no tape.
Sometimes I don't know who is writing the instructions. Like what plumber sticks a wax on a toilet bowl? I think only homeowners because they see the picture on the box.

 

[DanFL]

James - I'm not sure... I'd guess this was written by someone in China and translated to English. Given the pic in step 4, I don't really trust the instructions, so that's why I'm here. I'd much prefer one of the bigger US companies for the fixture, but not an option here. Also, this spec sheet says it's NPS: https://media.kingstonbrass.com/pdf/technical/specs/kingston-brass-AE8157DL-spec-sheet.pdf

Terry - 1/2" copper will not fit inside the nipple.

 

[James Henry]

They make a variety of NPS to NPT adapters.

 

[DanFL]

I called Kingston Brass and asked about this configuration. They confirmed that the female fittings on the swing arms are in fact NPT. Only the nipple is NPS.
https://media.kingstonbrass.com/pdf/technical/specs/kingston-brass-CC3SE1-spec-sheet.pdf

So I can discard the nipples they provided and use a standard 1/2" brass NPT nipple. But doesn't it seem strange that they would provide an NPS nipple to be threaded into an NPT fitting? I asked them about it and they said this is intended to be mounted on the wall of a free standing tub with access to the back, as shown in step 4 of the instructions! I can't say that I've ever seen a tub with that feature, but I'm not a plumber...