I am not certain if the Ashtabula Bow Socket Company were the inventors. This is getting a little late for my period of knowledge. But I think the company name is that. Good luck you might try patent info. Bow Sockets were in the Horse Drawn trade they also were for top bow sockets for autos too. My 1908 car has brass ones but most were steel for the top wood bows. Model "T"s had them too.
I've got some of the vintage 1970's Astubula stuff here at the shop. We cleaned out under the back trailer a couple weeks back and came up with some stuff my Pop had thrown under there. Black oxide finish, stamped Astubula. I've got a matching stem and fork somewhere in addition to about 3000 fork forgings from Schwinn. I was under the impression Astubula was the company that made all the fork, stem and crank forgings for Schwinn but I could be wrong. Not sure but there could even be an invoice or two in the old filing cabinet my father stuffed with old receipts.
Yes they were and the black ones were heavy duty and for the then new BMX trade (Bicycle Moto Cross) They were forging experts and made the forks stems and cranks for Schwinn and others. I used to see their booths at the bicycle dealer conventions in the 1970's. But we are on ground that is far from the pre-1918 period that is the club's focus...just some of my ruminations.