Please help us identify this insulator! We were given an approx. time frame of manufacture from one collector of late 1800s - early 1900s. It is comprised of metal on the top (iron? steel?) and a composite material on the base, that inserts into the metal. It has a threaded pinhole and no skirt. The very top looks like a cap of some kind would have screwed on (it's threaded). It stands 6 1/4" high, the base is 3 1/4" across, and the top (where the cap would presumably go) is 2 3/8" across. Any information on its use and where they would likely be found would be appreciated. Also, if anyone owns a cap that they'd be willing to part with, contact us! Thanks!