In article ,
Stuart writes:
Can anyone tell me the difference between GU10 and GZ10 Mains Halogen
bulbs . The GU10 are described as aluminium . Is it to do with the
reflector ??

Yes.
GZ10 are dichroic lamps which dump a lot of heat back into the fitting.
GU10 are aluminium reflector lamps which direct more of the heat out
with the light beam.

You can use GU10 lamps in GZ10 fittings, but not the other way round.
The lamp bases are slightly different and should prevent GZ10 lamps
being used in fittings not designed to handle the extra heat being
dumped backwards.

--
Andrew Gabriel