Power Wizard's Screw Tight Round Post Insulator (SKU: I-15) is designed to fit 1/4 to 9/16 in. posts and 5/8 in. fiberglass t-posts. Suitable for wires up to 5/16 in. diameters, this insulator, available in packs of 25, ensures a secure electric fence setup. Choose Power Wizard for reliable and durable round post insulators that elevate the performance of your electric fence.