These Field Guardian Wood Post Nail-On Electric Fence Insulators are perfect line insulators for permanent fencing with wood posts. The nail on insulator set is great for wire, polywire, hot coat, and polyropes up to 3/8 in. The rounded form and special materials make the electric fence insulators resistant to mechanical wear and efficient even when used with the most powerful energizers. The insulators are especially great for use with low impedance energizers and high tensile wires.