Picture nails were used in Victorian homes to hang pictures. Since many pictures were hung with the use of a wire, and before there was anything like wall fasteners, a stout nail with a pretty head was used to hold the wire. The designer head came in various sizes and patterns.
This nail is 2 1/4 inches long. The brass-button top measures 7/8 inch round. The nail shank is threaded so it can be removed from the head. This particular pattern is different. Check to see if you have one of these.