Twist-Lock® receptacles combine functional design features, unparalleled quality to deliver ultimate performance. The high-impact nylon face of each Hubbell Twist-Lock® receptacle has a colored ring. Keyed to an internationally recognized color coding scheme, this ring enables mating devices to be matched quickly. It's just one more example of user-oriented thinking at Hubbell. The terminals in each Hubbell Twist-Lock® receptacle are mechanically and electrically the finest available. These terminals incorporate unique design features to contain and hold conductors, including an external back wiring "wraparound" clamp, a wire restraint recess and more. The materials used in every receptacle are of the highest quality. The all brass mounting system provides a safer, lower resistance ground path than those made of steel. The thick wall base is constructed of an engineered thermoplastic to offer the benefits of a thermoset, yet with much greater impact-resistance. Hubbell Twist-Lock® Receptacles: Voltage color coding on the outside. Proven designs and quality materials on the inside. Any way you look at them, they are the standard of the industry. 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 and greater resistance to corrosion than steel-mounting systems