To answer Trumpys' question from this thread:

https://www.electrical-contractor.n...bb=showflat&Number=170227#Post170227

I believe that there were varying distances between mounting points in the 1950s & 1960s until 84mm became standard so the manufacturer (HPM in Sydney, Australia) supplied the outlets & switchplates with different mounting holes so the installer could select the pair of holes needed to affix the plate to the mounting points.

I haven't tried to push the knock-outs from the plates as I have no intention in mounting these items. When I do mount these outlets, they'll go on display boards & be held with silicone as not to damage them.

The large square outlet at the top has four sets of mounting holes for either use in 1 gang (84mm apart) or 2 gang (46mm apart for the width of the plate & 84mm apart from top to bottom) though it was not common to find many items on the 115 x 115mm plates (4 1/2 inches approx)