I agree with Gary. I have never seen a shower arm that is not 1/2" NPT.
However; I would use vinigar, I think it works better than CLR.

Rob.


"David Hare-Scott" wrote in message
u...

"Willow" wrote in message
...
Hi

What's the best way to clean rust & hard water grime off a pipe thread
in
the shower? I need to replace the shower head, but the replacement
bits
won't fit, despite the thread being the same size.

Any ideas? I'm onto my second application of CLR, don't know what to
try
after that.

--
Wanda
aka Willow

I doubt that a build up of grime is the cause of the problem. If an old
fitting came off then the new fitting of the correct type should go back
on with little or no effort. I think that the fitting you have is not
the correct thread. As somebody else said you may need to replace the
whole arm (if it has an arm) as joints internal to a proprietary
assembly may not be compatible with standard fittings.

If you cannot work it out call a plumber as forcing the wrong fitting on
will just damage your existing plumbing and make the job more expensive
to finish.

David