Simulated Opal Stud Earrings These Stud earrings are handmade with 4mm Fire and Ice Simulated Opal balls. 4mm is about the thickness of 2 nickels (Please see reference photos). The posts are 925 Sterling Silver, 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). Shipped in gift box.