Back box lugs and cross threads.

[davesparks]

These must be seriously old, 3.5mm been about for decades (don't know how many though).

I think they changed at around about the same time that cable sizes changed to metric, as i only ever come across them in installs with imperial cables. I don't the exact date of the change but the 14th edition was reprinted in metric units in 1970 so that should give a rough idea

 

[Barry White]

A couple of my upstairs back boxes were black japaned boxes with 4BA screws fed by slip tube conduit. They are still there somewhere (plastered over) The switches are on the other side of the door now. Unsure whether the hand of the doors was changed after the rewire or before but switches were behind the door.