I see 4 Ring Grip plugs and HPM's first attempt at a side entry plug there from the late 40's/50's. I'm a chronic hoarder of things old and such fittings look the part in my 1931 wired house with split seam steel conduit and fabric covered VIR wiring
I've got dozens of bakelite plugs, polarity reversing double adaptors and other currently 'frowned upon' fittings in use. You get boxes of bakelite fittings like that at the various markets/swap meets/junk shops here. We won't mention the first generation of HPM plugs will we...the ones where a loose strand of wire pokes out from beneath. I received my first shock off one of those!