(I'll assume you meant 15mm, not 12mm - metric are outside diameter,
imperial are inside IIRC)

And for a followup, putting fittings on a pipe which has been expanded by
frost.

(ans: get a solder fitting, press a suitably sized socket into it to make
it
larger. Maybe do this in a couple of stages)

(of course this won't work if 1/2" pipe is smaller - I don't know...)


oops, yes 15mm, sorry.
Thanks for the tip Clive.
David