The IDEAL WIRE-NUT wire connectors are the original twist-on wire connectors and feature a positive-grip design for easy installation. Five color-coded models cover hundreds of wire combinations. The fixed square-wire spring provides a secure connection that won't relax over time. 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 UL listed to 486C and CSA certified to C22.2 #188 Minimum wire capacity of one # 18 AWG and one # 20 AWG, Maximum wire capacity of two #14 AWG Compliant with federal specification w-s-610E Reusable for easy circuit changes and additions