Screw tight round post insulator. Self-centering post cavity with spin-on nut will accommodate round posts ranging from 1/4 In. to 9/16 In. Dia., and 5/8 In. fiberglass T-posts. Extends wire 1 In. from post. Installs without tools. Adjustable while current is ON . Made of high density virgin polyethylene plastic with maximum UV (ultra violet) inhibitors for long life. 25 per bag.