Gold Filled 6mm Outside Diameter CLOSED Jump Rings.  These Jump rings are guaranteed Gold Filled made from wire manufactured right here in the United States.
 
Please note the lower the gauge, the thicker the jump ring.

Gauges:
18 gauge - (Thickest) ~ 1.1mm thick - Great for adding charms to charm bracelets or attaching toggles to chain. Very durable and almost impossible to open up without pliers.