Black Onyx Sterling Silver Stud Earrings. These Stud earrings are handmade with Natural Black Onyx Cabochons and 925 Sterling Silver. The posts are heavy duty and slightly longer than standard (.036/19 ga. x 7/16"L). Two types of 925 Sterling backs are included for preference or just to have a backup pair (Rubber core bullet style and traditional friction catch). Free polishing cloth safe for all types jewelry included. Shipped in gift box. 4mm is about the thickness of two nickels. 5mm is the size of a small green pea. 6mm is the size of a large green pea Please see size reference photos. Visit the Salish Sea Inspirations Store from the link at top to learn more and view all my offerings.