A Cartier emerald and diamond clou stick-pin

A Cartier emerald and diamond stick-pin, the pin in the form of a nail, the head and the point set with calibre-cut emeralds and old-brilliant-cut diamonds, set in platinum and yellow gold, bearing French platinum hallmark and signed Cartier with inventory number 51AY, length 5cm gross weight 2.1 grams, circa 1920,