The Plug from a Pinball Machine
This techie took a photo of the plug from a pinball machine that they’re trying to refurbish. And judging from its shape, the plug most likely dates back to the 1960s. But this type of plug comes with 2 parts and the part that’s missing is the one that has openings for the prongs that screws on. But if that’s the condition of the plug, then the pinball machine is probably in even worse shape.