Bigfoot1 is right, it is "hardware" (a swivel-snaplink), and being so large (see the nickel in the photo for size comparison), probably for a sailing-ship's rigging -- although of course it can be used in non-Nautical applications. Long ago I worked at a "Nautical Hardware" supply-company, where I handled many such objects.
Having an anchor marking does not automatically mean an object has a Nautical purpose. Nhbenz is correct, that particullar anchor marking is the trademark of the North & Judd Manufacturing Company ...which first began using that distinctive mark in 1878. Their trademark anchor-stamping is found on an enormous variety of the North & Judd Mfg. Company's brass products, notably including horsegear (like spurs) and buckles, also including some Military ones. For more info on that company, go here and scroll down to the last paragraph of the page's text: Antique / Vintage Buermann Horse Head Spurs Sold By N&J