Regarding carriage bows and bow sockets, as mentioned by bbattle: They were the structure for the fabric tops of carriages and buggies, which came to be called "top bows" with the advent of the automobile. I presume these are still in use on convertibles, though in a much-articulated and power-assisted form.
Even on hardtops, sedans and station wagons, there was a kind of top bow used to attach the headliner to the roof structure, right up to the '70s. Somebody had to make them...