Would like to know what this is called. Use/application. Circa? And appox value. Thank you.

Lou Hall (and others) said:

That is a street lighting hanger. The light was suspended from cable which was attached to poles on either side of the street.. The metal bracket in your picture was attached (clamped) to the cable. The light fixture base screwed into the insulator . Sometime there was an intermediate piece that screwed into the insulator and had a hook for attaching the streetlight fixture. My guess is that this is an early 1900's piece. Value somewhere in the 50-75 dollar range