Hubbell - HBL2330Locking Devices, Twist Lock, Industrial, Single Flush Receptacle, 20A 277V AC, 2 Pole 3 Wire Grounding, NEMA L7 20R, Screw Terminal, Nylon face, Back and side wire, Black. Wire restraint recess for both back and side wiring, greatly reduces the possibility of loosening the terminal connection Face color coding by voltage facilitates locating and mating of proper devices All brass mounting and grounding system provides a lower resistance ground path