These receptacles date from when I was forming my very first memories....so forgive me if I am not quite correct. I seem to recall that these receps were the equivalent of today's 20 amp 110 receptacle. Both slots were "T" type so the plug could go in either way, or different plugs could fit. There were no "standard" plugs at the time, and even polarity (neutral prong being larger) was a sometimes thing.
