An electrical plug selectively insertable into receptacles having different configurations of apertures for effecting selectable electrical connections. A plurality of contact prongs have extended positions in which they project exteriorly of a housing. Each of an appropriate subset of these prongs is adapted automatically to sense and enter matching apertures of a selected receptacle. The remaining prongs during such entry are moved inward of the housing by contact with and movement relative to a surface of the selected receptacle adjacent to the apertures, and cause prongs of the subset to be locked in their extended positions as they enter the matching apertures.