These are good quality insulators that screw into wooden fence posts and will hold tape up to 40mm wide or rope up to 6mm diameter. Both 20mm & 40mm tape can be used and slot into the top of the insulator, the tongue is then pressed shut and clipped over at the top to hold the tape securely in place. Alternatively, rope can be used through the guide hole for rope or twine, these insulators will take rope up to approx. 6mm and again the clip just locks the insulator closed at the top to hold the rope in place. The thread on the insulator's screw also has a notch cut out of it making it easier for it to bite into the wood when being screwed in place. Ideally suited for most tape fences and the main advantage over insulators that hold tape loosely is that should the tape break for any reason then the remaining tape will not flap around destroying itself. The fence line will still be in position apart from the area which has broken.