ss16 - 4mm Flat back 2058 Swarovski rhinestone crystals are the most popular size for general use, they are perfect for making wedding stationery with or for accessorising handmade cards. Our 4mm rhinestones are part of the Swarovski Elements range of crystals. They have a multi faceted crystal glass face that has a higher lead content than other crystals which increases their refraction index making them much more sparkly. This sparkle is increased by the silver foil backing that not only acts as a good surface for bonding to, but reflects light back through the crystal.