In article .com,
wrote:

I wondered about that. A lot of the fittings from the plumbers
merchant come with copper ones for some reason, but you can only
buy copper ones in large quantities and the sheds only seem to
have brass ones. Brass are harder, and apparently give more
support to the pipes. Copper are softer, and seem to require less
tightening. I'm sure both should work OK.

Copper olives seem to come with fittings which are
all plastic. Eg, Some Triton electric showers.
Instructions= "hand tighten only" On our bleeding
mains pressure? You must be joking.

I notice also the copper olives don't work very
well if you try to use them a second time. Probably
work-hardening of the copper.

--
Tony Williams.