These 5mm sterling silver jump rings are open. The 18 gauge rings are nice and heavy, strong enough to stay closed once you have finished your project. Although not as secure as closed rings, the open rings are very versatile. Make sure to give a little extra squeeze to the ring once you have looped it--this will help keep it closed. Measurements: 5mm outer diameter. The wire is 18 gauge, or .040 inch thick. Quantity: 10 Jump Rings.