It appears to be an iron version of a garter-clasp, just shaped slightly differently from what you see in the circa-1900 advertizements below. Please note, the ad calls it a clasp, not a buckle or a snap. As the Boston Garter ad also shows, they were used by both men and women. Before the term "socks" came into use, the term was "stockings." (Our stockings were hung by the chimney with care, in hopes that Saint Nicholas soon would be there.) And millions of men wore these garters. Before elastic-fit socks came into being, you needed those garters to keep your socks from falling down around your shoe-tops.