Posting a message to the forum will remove the above advertisement
  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  2. Checkout our Plumbers Insurance area - heavily discounted Public Liability Insurance and Van Insurance specifically designed for plumbers.

Discuss How to join threaded brass fittings in the Fittings & Pipes area at

  1. Chris 11

    Chris 11 New Member


    I'm fitting a new shower valve (Grohe Rapido T universal) it has 1/2" inlet and outlet ports to connect to so have got some 15mm x 1/2" male unions (I think that's the correct term) both straight and elbows. I've tried to find out how to fit the brass fittings and there's lots of conflicting info out there (perhaps some of it is US so based on NPT - but I'm pretty sure these are parallel threads). The questions I have are:
    1. Should I use anything on the fittings (PTFE, pipe dope)
    2. The elbows seem to go in hand tight and then stop after about a quarter turn with a spanner so how do I get them to point the direction I need them to
    3. Probably hard to answer this but how tight should they be

  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    yes they need somthing

    loctite 55
    loctite 577

    for me either 577 or 55 would be the option if you use pfte put enough on and with all methods leak test before you fill the wall in / tile
    • Useful Useful x 1
  3. Chris 11

    Chris 11 New Member

    Thanks Shaun. With using loctite does it mean the threads can be just hand tightened in which case I can point the elbows anywhere I like even if they are loose before applying the loctite
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    577 can also if you put the right number of turns on 55 can (it won't be hand tight you will need a spanner or grips etc)
  5. marvoni

    marvoni Active Member

    Some of the NPT (fuel) threads, also know as 'dryseal' can be use without any sealant but TBH I've never had the nerve to try it any usually use PTFE tape.
  6. Chris 11

    Chris 11 New Member

    Tried to find somewhere that had 577 which looked like it was probably the easier and possibly better option but couldn't find it locally so got some 55. Seemed easy enough although I think I put one on the wrong way around as it shredded it a bit before I got used to which way around to do it! I'll see what happens when I leak test it but it'll probably take me a few days to get the rest of the pipe work in place ready for that. No idea if any of the connections are tight enough but given all the warnings about don't over tighten I've tried to go on the side of not killing it and if it needs more when I test it will adjust then
  7. Chris 11

    Chris 11 New Member

    Thanks for the info Marvoni but that sounds a bit beyond me. I'm just working on a shower valve and I don't know if you can get NPT (tapered which would be BSPT in the UK) threads for shower valves. I'm pretty sure mine are BSPP (parallel). NPS would be the equivalent in the US system according to a web search but although they are the nearest equivalent in the two systems it says they are not compatible
  8. fixitflav

    fixitflav Active Member

    Here's some data on pipe thread if it's any interest.

    Attached Files:

Similar Threads - join threaded brass Forum Date
Hi all, Just joined... New Member Introductions Nov 18, 2018
Leaking push fit joint Plumbing Forum Nov 14, 2018