This is a sewer lid that is identified only by it's design, a direct descendent of the early Manhattan DPW spoke and wheel caps. This one could be from almost any time in the first half of the 20th century.
The wheel and spoke design here has 8 spokes in the center and 16 spokes in the outer ring and where earlier designs had text in the middle ring this one has 8 raised vent holes. Vent holes are always a good indicator that it is covering a sewer opening!
Probably from the New York City Department of Sewers.
This cap is in the Fulton Landing area of Dumbo Brooklyn, but similar designs are found throughout the city.