These probably were "Brown's Pony" insulators. Their claim-to-fame was so that extra wires could be mounted on the same crossarm (beneath). These hole-through insulators required a special pin which had a standard topside with threads underneath for the "Brown's" insulator. The latter was designed so that it would resist sticking to its pin owing to wood pin moisture swelling. This openwire practice and the Brown's insulators found scattered but rather limited use throughout North America on phone openwire leads.