Ross-Simons - 16.5-17.5mm Cultured Biwa Pearl Ring in Sterling Silver. Size 6. Take your look to the next level with this organic and eye-popping style! The ring boasts a 16.5-17.5mm cultured biwa baroque pearl in a sterling silver bezel. Pearl is unique and will vary. White biwa pearl ring. Pearl birthstones are the perfect gift for June birthdays.