21 ELECTRIC EQUIPMENT AND PARTS THEREFOR-NAMELY, ELECTRICAL CABLE CONNECTORS; WALL AND BOX MOUNTING RECEPTACLES AND ACCESSORY EQUIPMENT FOR THIS TYPE OF PRODUCTION-NAMELY, DUST-CAPS, JUNCTION BOXES, PLUGS AND SPECIAL FLANGES [ ; SPECIAL FUNCTION SOLENOIDS; ELECTRICAL RELAYS; ELECTRICAL SWITCHES AND PUSH-BUTTONS; AND INSTITUTIONAL SIGNAL EQUIPMENT--NAMELY, CALL STATIONS, ENUNCIATORS, CORRIDOR PILOT LIGHTS, PAGING SYSTEMS, AND EXPLOSION AND VAPOR-PROOF SWITCHES ]