Randy,

Is there continuity between the vertical pole of the crowfoot and the mounting strap?

I've never seen one of these referred to as a "grounding" receptacle in old catalogs and textbooks. They are always described as "3-wire polarized", but they seem to have been used the way we use a NEMA 5-15 today. How was this one wired when you took it out?

About 90% of housing stock in my area is postwar, so I don't see as much of this kind of stuff. I have been hunting for a receptacle like the one in the first photo, which does look functionally equivalent to a T-slot. (The parallel slots don't appear to be polarized.)

The crowfoot shown does appear to have about the same blade spacing as the 1-15, and we already know that a 1-15 plug can be mangled to fit an Aussie receptacle, so this must be the parent pattern. (Of course, this may be a later iteration.)

Interesting that we had this pattern way back in the '20s, and we could have gone with it and had grounding receptacles from the beginning, as Australia and New Zealand have. But no, we had to wait 40 more years, and now, forty years after that, there are still millions of buildings out there with ungrounded receptacles. Oh well, more work for us, right? [Linked Image]