Before my time in the audio industry Cannon (now ITT Cannon) made a Type O connector with an oval shaped body. The Cannon RJC-8-1955 catalog said “This series consists of a line of 3-contact oval-shaped plugs and receptacles, equipped with Latch Locking Device. Contacts are silver-plated, full-floating, non-twisting, with a 30 a. current rating. Solder terminals are tinned for ease of wiring. 30 a. contacts accommodate No. 10 stranded wire. 2400 v. flashover.” While Cannon sold these for microphones, they were no longer in use when I started in audio in the early 1960’s.