a converter plug with improved self - locking terminals that are adapted to interlock with the terminals on a standard electric plug when the prongs of the latter are inserted into openings in the converter plug and the standard plug is rotated through an angle with respect to the converter plug for causing its prongs to interlock with the converter plug . novel means is provided in the converter plug to prevent the displacement of the electrodes therein when the electrodes on the standard plug are inserted into openings in the converter plug and the standard plug is rotated with respect to the converter plug for causing its terminals to interlock with the terminals in the converter plug .