Contoured wing profile brings more power to every twist for fast, secure connections. Expanding, square wire spring accommodates a wide range of wire sizes and combinations. Flame-retardant shell. Tough, UL 94V-2 flame-retardant shell rated at 105 °C. - Live-action spring expands to accept wire shape and size with no pre-twisting required. Square-wire spring threads directly onto conductors for fast, secure connections. Deep skirt helps protect against flash-over and turned-back strands for maximum dielectric protection.