Insulators allow you to fasten electrified wire to posts without losing energy through the post. The Zareba 4-inch Fin Tube Insulator is made of durable, non-conducting UV-stabilized polyethylene. Designed for use with steel wire, the fins of this insulator prevent slipping, holding snugly in place. Its extra thick walls prevent-voltage loss. 25 per package.For wood posts Secure insulator with 2-inch barbed staple (staples not included). This product can be used with high tensile fence systems.