That is a common wood strain used by the millions by most city trolley lines and many other electrified rail operations; usually at a nominal DC voltage of 600. One catalog that I have (O-B) lists them in lengths from 6 inches to 48 inches. They were manufactured by Ohio Brass, Westinghouse and others. As to age, I have a 1907 catalog that lists them and they were made as late as the 1970s. I would guess that they were in production for almost 100 years, beginning during the 1880s. This is an educated guess based on a long-standing interest in trolleys and viewing many pictures of early trolley installations. (Info courtesy of Dave Kingston, Ft. Lauderdale, FL)

I have a piece like that and it was part of a street light assembly in northern new york.....it was part of light unit where the whole light was lowered by chain to change bulb....(Info courtesy of Gary Scott)

These strains were catalogued by Ohio Brass from the late 1920s through the 1950s (Info courtesy of Jimmy Burns)