Looks like someone forced a inch size nut onto it.
It has been hammered but not really beaten (you can see the 'flat' on end)
It's a pretty standard part, almost every drum rear brake uses a standard 19mm 'shoulder with 8mm thread.
The 'shoulder' lengths change slightly but a washer will take up any excess length.
It wouldn't be a real big deal to make a stainless steel one, in fact, I probably will as I have some 5/8" hex stainless
