I have yet to see these in use but a friend of mine told me they are used a lot. These are a simple design of wire holder made of Nylon. What's neat though about them is that they had a matching plastic key to help turn them into the wood on the top. Someday I'd like to find one but the only place you can get them from is a distributer. A lot of them don't want to deal with an enthusiastic insulator collector but with a contractor. Go figure. From L-R: Chance, Black, Dark grey, Have a circle in top with clock code, Hubbell in black, Joslyn Grey, Black and Lt. grey, Have 4 rows of hole grips in top, Last is a MacLean power Systems black, Has two rows of hole grips in top. Bottom picture shows the tops. A matching key fits into the holes in the tops to help turn the insulator into wood etc with pliers or wrench.