Be surprised if anyone has seen one like this

When working for AT&T in the late sixties wrecking out long distance lines that were erected in the 1920 s. I came across these insulators, they held the wires apart over long spans. Me and my work partner decided we would try to salvage some. Wow tough, had to cut both wires and let them down to the ground at exactly the same time. If one wire was to lose it would break the ends off. Then if you were successful you had to hike down in the canyon to retrieve them. We managed to save four. Anything you can tell me about these? Thanks Don