This is used on the coils for a 1960s Tech TE-15 "Tradiper"; Coil diameter is about 17mm; pin length is about 10mm; the four pins form an inverted "Y" in the photo. I think I've seen similar plugs in old radios; as dry battery connectors and as electro-dynamic speaker connectors. As I remember, they were simple discs of phenolic with pins rivetted-in. They are not DIN or XLR4. Like many/most dippers, these had the coils in a plastic/Coolite tray which is no longer present; I'd like half-a-dozen sockets to make a storage rack as I did with my home-made GDO years ago. I'm not sure that they do have a formal name; if they do, I don't know it (yet).