What is this called and how is it done?
Looks like an Xcelite series 99 tool, probably formed by swaging? Not sure what that part would be called.
Here’s a link to a patent that calls them “keys”
The patent was granted in 1949 to J.N. Petre of Orchard Park NY and John O. Olsen of Lakewood Ohio
Mr. Petre likely worked for the Park Metalware Company of Orchard Park NY - makers of Xcelite tools back then - before the company was sold to Cooper.
Prior to the Internet - I would have had to have spent days searching patent office archives to find what Google located for me in a few minutes of searching.