odd insulator

[GuntherHess]

I found an odd insulator it looks like a common green brookfield insulator with the top cut off. It says something like 2 part transportation on it. Apparently its one half of some 2 part insulator. Anyone seen anything like this before?

 

[GuntherHess]

It actually says TWO PIECE TRANSPOSITIONAL on it.
I found some info on it.
http://www.hemingray.info/database/cd/190.html
Looks like the base of one of those. Dont know if its hard to find or not.