Ordering the wrong size happens now and again.
This week a new customer ordered 18ga 10mm ID silver plated jump rings to match some existing jump rings in their stock. When the customer received their order, the rings were too big. The correct size should have been 8mm ID. The confusion lies with bead catalogs using Outside Diameter and chain maille suppliers use Inside Diameter. The customer wanted 10mm O.D. not 10mm I.D.
Most bead catalogs list their jump rings by Outside Diameter. This sizing method is flawed when applied to chain maille projects. We offer outside diameter in the product information box as a courtesy, but we encourage you to rely on inside diameter. We have made our best attempts to reduce these errors by offering a downloadable visual guide to ring sizes.
So we suggested that the customer send us a sample of the their jump ring and it turned out to be a 16ga 7.0mm ID. If you think estimating ring diameter is a challenge, wire gauge (thickness) is impossible. I have been in the business for 15 years and I still rely on a wire gauge. Measuring gauge is difficult because wire is too small for a ruler and the reflective surfaces fool the eye. Shiny jump rings and dull jump rings appear to be different sizes when held up together.
So what is the best way to estimate gauge?
We recommend every wire artist have a wire gauge in their tool kit. Be when you don't have that tool handy, you can estimate wire thickness (AWG) common items.
U.S. Penny - 16ga
U.S. Dime - 18ga
Credit Card - 20ga