Thanks. I'm glad you liked it. This catalog also gave me a clear look into early American plug technology. I was told appliances could either be hard-wired or fitted with an Edison base. There might have been other plug-socket schemes,but Hubbell's won out.
It's interesting that he started with a tandem blade design, then for some odd reason settled on the parallel blade (NEMA 1-15 or 125V/15A) design that we have to this day for household use.
The tandem design was not discontinued,but assigned as a NEMA 2-15 or a 250V/15A plug.
For a while 120V outlets were designed to take both. Here is a 1940s era socket in my bathroom.