Strange Brown Bakelite Art Deco Plug Receptacle

I just love all the Art Deco detailing on this outlet but it’s the back that makes it interesting. Rather than a strap to attach it to the junction box there are two places where it apparently snaps into some special kind of mounting. I’ve never seen one like this but perhaps you have them in your vintage home? Or perhaps an RV or mobile home?

There is no manufacturer noted anywhere. Missing one brass terminal screw that is easily replaced if you need it.

 Marked: 10A – 250V and 15A – 125V