DIN connector
The DIN connector is an electrical signal connector that was standardized by the Deutsches Institut für Normung (DIN), the German Institute for Standards, in the mid 1950s, initially with three pins for mono, but when stereo connections and gear appeared in the late 1950s, versions with five pins or more were made. The male DIN connectors (plugs) feature a 13.2 mm diameter metal shield with a notch that sets the orientation in which plug and socket can mate.