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. Makes quick secure connections for positive continuity tightens without ratcheting yet removable for re-use.