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