Finally, a complete one

[TinCanAlley]

So, I have gotten my hands on several of these old in-wall radio antenna sockets, but this is the first one that has the original plug. I've cleaned it up, but it still has some old paint in areas that are quite hard to reach. I think I'll leave it as is so as not to damage it. From a reasonable distance, it looks pretty new.

What I need to know is what kind of wire is needed for the plug. Is it just your standard cloth covered wire? The hole in the plug is kind of oval instead of round, but maybe this is so the wire fits snugly?

Also, I found no markings to help determine age. It was removed from an apartment in a building that was built somewhere between 1938 and '41. The socket was connected to blue wire (not cloth, but pretty old) and went up to the attic of the building. There was a long copper wire that has long sagged and fallen.