While this "key" usually remained in the fixture, you turned it like a key
Ah, thanks. So were these like the switches still commonly found on tablelamps, where you keep turning in the same direction for both on and off?
I don't think that latter type was ever used here in England. Switched lampholders had either a pullchain, or often a pushbar right through -- Press in on one side for on, the other side for off.
