Tight, square-wire spring threads directly onto conductors for fast connections with no slip. Tightens without ratcheting, easily removed for repeat usage on same size combination or larger. Fluted shell surface permits a firm grip for easy finger-tight connections. Thermoplastic shell shields against environmental extremes. Flame-retardant properties resist heat distortion up to 221° Fahrenheit. Superior flash-over protection. High-dielectric shell features deep skirt design to prevent exposure of bare wire. Buttress threads screw into wire insulation. For copper to copper connections only. GB-2 Blue: minimum 3 #22 - maximum 3 #16 GB-3 Orange: minimum 3 #20 - maximum 4 #16 with 1 #20 GB-4 Yellow: minimum 1 #14 with 1 #18 - maximum