The Easy-Twist WWC-G-SJ 50-Count Small Jar of Grey Winged Wire Connectors are designed for use on copper wires in the 18-8 AWG size range. They???re made of flame-retardant thermoplastic rated for a maximum temperature of 105?? Celsius (221?? Fahrenheit). The quick-grip square spring design grips in fewer twists and can dead-end a single wire; while the ergonomic swept-back wing design and ribbed texture makes them easy to twist. Their compact design is useful for applications in tight areas or anywhere else you need to connect wires.