Same answer as Sweden. Metal ones ? old ones seem to have no limit at all, didn't have the chance to take a look at a new one. Used almost everywhere, except for small table lamps, etc (ES 14), only exception being fluorescent tubes and metal halide elements. Compact fluorescents with ES 27 (E27 here) screwshell are pretty common. It is, as far as I know, strongly recommended but not mandatory to wire the phase to the bottom contact.
