I have some of the 10-20 fittings, mostly Hubbell. They were used around here for 110V
grounded recepticles in barns, for cream separators and general purpose. Last I used them were for 12VDC portable wiring, and easy speaker disconnects.
FWIW, our place was first wired in the early 1950s, and had those installed with grounded wiring, in the barns.
