This is going to generate so much debate, but I 100% know the answer. It's a 42 insulator for 10 pin cross arms telephone poles. My Dad was a lineman who worked on them. ❤️ This is an insulator for electric lines used on poles, also for telephone wires. I have a few around here. Oh For god sake .... Don't hit with a hammer......!!!!! It will shatter in a million pieces of glass...!!!!
SHARE if you remember what it was :)