Here is a nice setup. The lag screw anchors the yoke into the tree, the insulator is tied to the yoke, and the pin comes down and holds a split porcelain insulator, which is held together by a wrap of wire around the tips of the holder than comes down from the pin.

You get the insulation of a double petticoat insulator, and the wire is free to slide in the split porcelain insulator.

Nice that it's a CD 160 Hemingray too, as I'm a Hemingray collector :-)

This setup is called the "Holmes Tree Insulator" and is covered under the patent:

http://reference.insulators.info/patents/detail/?patent=U-626065

by Welles F. Holmes in 1899