The original twist-on wire connector features a positive-grip design for easy installation. The fixed square-wire spring provides a secure connection that won't relax over time. The positive grip design provides fast, easy installation with no pre-twisting required. The deep, wide skirt helps protect against flash-over and turned-back strands for maximum dielectric protection. wire connectors are reusable for easy circuit changes and additions. Tough, UL94V-2 flame retardant shell rated at 105° C (221°F). UL 486C Listed and CSA 22.2 #188 Certified; comply with Federal Specification W-S-610E and is classified in accordance with IEC Publications 998-2 and 998-2-4.