This question was asked up the thread.
JB pretty much answered it. Thought I would add a little.
First known records on hubs was 1928 (As JB said) in the USPC records. Hubs was probably made at USPC in Cincinnati until 1948. Burt in Portland, MA bought the USPC molds in 1948. There was stink over USPC making chips after Burt bought the molds. Maybe we will never know where some of them were actually MADE. Mason had exclusive rights to the hub, but from what I know about other molds we may never know for sure that they were the only Co to distribute them.

The hub could be made today. I would guess it is an open mold at this time. Mason Co is still in business in Chicago, but they do not sell chips.