Use American FarmWorks 5 in. Nail-On Extender Insulators for 9-12 Gauge Polywire and Polyrope with your wooden fence posts. These electric fence insulators can be used with traditional steel and aluminum fence wire gauges 9-12, as well as with polywire and polyrope up to 1/4 in. in diameter. Use these yellow 5 in. extender insulators to avoid losing energy through your fence line to keep your fence performing to the best of its ability. These electric fence post insulators extend the electrified wire 5 in. from the wooden post. Each fence insulator is made of UV-stabilized polyethylene to prevent damage from the sun's rays.