These are 12 mm (6.84 cts, or 7/16" diameter!). They are striking round clear studs of nearly 7 cts each and mounted in rhodium-plated .925 sterling silver with a butterfly backing on the post. Description only applies to the 12 mm. Show off!
Also available are smaller studs of 10 mm (3.87 cts), 7 mm (1.28 cts), and 5 mm (.46 ct). FYI--The smallest ones have a diameter of 3/16".