The type of insulator you need (to hold the fence material on the post that supports it, while preventing the fence from contacting any surface that will cause current to leak) is determined by your choice of electric fence; most manufacturers market insulators specifically suited to their fence products. In general, braid, rope, and coated wire are installed on insulators that allow the fence to slide through. To help prevent chafe and wear on a tape fence, however, insulators need to be the type that clamps and immobilizes the tape (especially important in windy areas), and to be installed vertically on the fence post. Avoid cheap "generic" insulators (often made of brittle plastic), which only last a few years.
