These insulators have a large spark flange around the base, and the wire is held further away from the post compared to other H-T insulators. The wire is held in a slot by a removable pin with plenty of space for wire movement to keep line friction to a minimum. The wire can be removed from the insulator while it is still under high tension. This allows the wire to be easily dropped from about 4 posts to drive over it occasionally.
These insulators have two holes for either nails, wood screws or staples to make a strong attachment to the post. The plastic is very high quality - tough, not brittle, even after many years of weathering in sunlight. These insulators have the strongest designs and quality plastic needed for the abuse and life that the normal high-tensile fence is expected to handle.