Authentic 18K Yellow Gold Tiffany & Co. Diamond Classic X Ring Band. This beautiful piece features 15 brilliant round diamonds totaling .18 carats. The top of the ring measures 3/8 of an inch wide. The ring is a size 5.25. Sizing is available for an additional charge. It weighs 6.5 grams. MARKED: Tiffany & Co, 750, 1990..