I found this at a local flea market. It is 4" tall and 2˝" in diameter. Top is marked with incuse G.P.Q [note periods] (or is it G.P.O. with the last period too close?). It looks European (British?). The material looks and feels more like the stoneware baking dishes my wife uses from The Pampered Chef than it does any dry- or wet-process porcelain insulators I am familiar with. And the threaded pinhole is really narrow—maybe ˝" to 7/8"—but I can't get down in to measure accurately. Anyone have any info as to origin, manufacturer, use, value, and perhaps how it came to be in Brunswick, Maine? (I can guess that the P.Q could possibly stand for Province of Quebec given the location, but it's a wild guess.) Thanks for any help.
Answers: Thanks very much to Brent Burger, Bob Berry, Joe Maurath, and especially Rob Wilson from New Zealand, who had this to say:
"Your insulator is marked GPO, (General Post Office) it has the standard British thread 5/8ths which fits to a metal pin. It would have been used in British Isles, it is quite commonly found over there, and many are still in use--and as with most of these there is no maker but it is likely to be Bourne Denby. Salt glazed insulators have been used on telephone telegraph in UK since their earliest invention, alongside many glazed in white, or brownish glaze! How it got to the US is a mystery but maybe was brought as a souvenir by someone." Further, "these insulators with the 5/8th pin also included a rubber washer which was sandwiched between the pin and the porcelain body up inside the inner shed. This was the famous Cordeaux patent method of fixing insulators which has remained unchanged since it was first adopted by the GPO as the standard method of fixing and which gave its name to the Cordeaux shaped insulator so well used in UK and its colonies for over 140 years."
Bob provided this link: U-1565: http://www.nia.org/general/pifous/text/u1565.htm
Thank you everyone.