Positive-grip design requires no pre-twisting for fast, easy installation Use on bare copper wire do not use with aluminum Tough UL 94V-2 flame-retardant shell rated at 221 F (105 Celsius) Rated to 600-Volt max, fixed, square-wire springs create their own threads to maintain a secure positive grip that will not relax over time Product Specifications: Minimum wire capacity of two # 18 AWG, Maximum wire capacity of four #14 wires and one #18 AWG, UL listed to 486C and CSA certified to C22.2 #188