DESIGNED TO LAST: Wings are knurled for a sure grip and offset from centerline for greater twisting leverage. Square wire spring grabs and holds wires for secure connections. DESIGNED TO LAST: Square-wire zinc-plated spring instantly adjusts to the shape and size of the splice FLAME-RETARDANT TEMPERATURE RATING: Flame-retardant properties resist heat distortion up to 105°C / 221°F HIGH-DIELECTRIC: shell features deep skirt design to prevent exposure of bare wire STANDARD RATING: 600V max in building wire and at 1000V max in lighting, fixtures/luminaries and signs UL LISTED: Canadian and U.S. requirements COPPER TO COPPER connections only