I found these two in the wild with large fractures. All it took was a couple light hits with another insulator and the tops fell right off. I believe I read somewhere one time that linemen would hit the top of the insulator to facilitate easy removal. You can see what looks like a hammer hit on the dome of the 104. Is what I remember reading correct? Does this mean threaded glass over time became "stuck" to their pins?

Here is the article that I read:http://www.insulators.info/articles/cork1105.htm The last sentence of the third paragraph.