Thinking it may be a gold round clip from treasure or trunk from a ship sunk off coast of eastern sea dug from sand because of the hallmark that mimics western european 18th century marks or even 19th century .
My thought is that it is the size of a Morgan Dollar. Has a post so it either is intended to set in wood or leather. Is beveled so it likely was in a position where one piece of a something slid or might slide across the flat surface . . . but it does not show heavy wear. Has a flat side so it is indexed to rest up against a flat surface.
Base of a chair or table leg wouldn't need the flat clipped edge, so I guess a slide bearing from inside a desk or pocket-door?