Hey fishstick,
It's uncommon, I think. Pre-1900, I'd put it on the shelf. The 1865 patent was for the internal threading. These were the first generation of threaded insulators.
"The mark belongs to the Brookfield Glass Company, which actually began as a bottle manufacturing operation in approximately 1864 in New York City and eventually grew to make many different kinds of glass products. James Madison Brookfield appears to have been involved with this establishment in the earlier years, eventually buying the company from brewer Martin Kalbfleisch around 1869. His son William Brookfield, and later his grandsons, would also become involved in the company.
The production of electrical insulators rapidly increased in the late 1860s and ’70s, until the 1880s when most of Brookfield’s glass production was insulators for telegraph and telephone lines.
For roughly 57 years, insulators marked with “W.BROOKFIELD”, “BROOKFIELD”, and later, with only a “B”, were produced. The products were also marked with the Brookfield business offices addresses in Manhattan which were embossed on many of the earlier insulators and can be used to date the products, though some of the dates overlap: 55 FULTON ST (1868-1882); 45 CLIFF ST (1882-1890) and 83 FULTON ST (1890-1893)."
August | 2012 | OrangeNCHistory
Insulator Historical Timeline - 1870-1880
