B. M. 812

N 40.75333° W 73.98114°
74.763 ft.
Copper Bolt
Stone Step
Year Established:
Established By:
Good as of July 31, 2013
  • Official NYBE+A Description:

    West Forty-second Street. A 7/8 inch copper bolt in the top of the north end of the lowest granite step at the Fifth Avenue and West Forty-second Street entrance to the New York Public Library. The bolt is about 25 feet from the south curb of West Forty-second Street and about 25 feet from the west curb of Fifth Avenue. (Note 5, p. 89.)

This is one of those nondescript marks that are so cool simply because they're nondescript: most people wouldn't have the slightest idea what they were for, even if they did happen to notice that small copper bolt at the corner of the library entrance steps. Through survey mark hunting, Rich and I are clued in on these little infrastructure "secrets" hidden in plain sight!

This bolt was described in "Precise Leveling in New York City" by Frederick W. Koop, published in 1914 (surveyed 1909-1912). As mentioned in the official description, the bolt is as follows:

NOTE 5: A bench mark of this type is the top of a copper bolt 3 inches long, leaded vertically in masonry. It is usually set flush with the surface, but at times slightly above it. The letters B.M. are stamped on the top as shown: [illustration of bolt with B M stamped in a column, with a point punch in the middle]

Unfortunately we couldnt't find any evidence of the stamped B M. We assumed that the bolt has been worn smooth by all the foot traffic over the past 100 years!

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