Resin Replica that is! I had the opportunity to repair one of these unique insulators and made an extra resin copy for the show. One of a very few clear threadless insulators out there! See the historical description from the Google Doc: "The Telegraph in America: Its Founders, Promoters, and Noted Men." Arno Press, 1879

Here's the link (it's free, unlike the CD 786 Replica that you'll have to buy a lucky raffle ticket for a buck for...)

https://books.google.com/books?id=XXwfAQAAIAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false