My cousin just gave me this hanger today. It was found in an old out building in Yakima, WA. His father in law is a collector of old stuff. In fact I have about two dozen light carnival disks and a few other insulators from him. The hanger made my day! Will install it on a pole with three strings of six disks of light carnivals.

Does anyone know if it's a common hanger (or whatever it's called) and would it have been used on the line from Grand Coulee Dam?

Answer; it's called a three way yoke. Thanks for the info, Mike Parker and Bill Kuhar.