Simulated Opal Stud Earrings These Stud earrings are handmade with Simulated Opal Cabochons and 925 Sterling Silver. Choose 4 or 6mm diameter.(Please see reference photos). 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). Polishing cloth for all jewelry included. Shipped in gift box. Opal is the birthstone for October.