This one is thought to be from a trolley line. Have no idea where it was found or used. With the recent ICON discussion about cast iron insulators, I thought some might like a look at these pics. I did not see it on the NIA web page of cast iron insulators. Good collecting ... Robin Update info from Bill Kuhar: These were used mid span. The catenary was attached to the two hooks on top and the live trolley wire attached to the center bottom stud with various clamps. Ohio Brass was a big supplier.