The industry's standard twist-on connector with quality performance and durability. GB specifies this connector for a wire range of #22 - #16 AWG and recommends a wire combination of Min: (3) #22 wire and Max: (3) #16. It is blue in color for easy color code identification. Recommended for copper to copper connections only. Made from tough, thermoplastic shells which guard against hydrocarbons, diluted acid or alkaline solutions.