A friend has a few insulators from his grandfathers collection, some of which he has never seen before. Can anyone help him identify this thread-less glass piece?

I think he mentioned his grandfather worked as a mechanic at Grand Coulee Dam

It was made with an angular skirt and has what appears to be electrical burn marks to the side-bottom of the odd wire groove.

Answered--Light bulb cover, most likely a part of a bigger piece or something, held into place with a metal bracket of some sort. I've seen these before and that was what I was told they are......Mike Herron