Durable and beautiful chain maille supplies by Weave Got Maille include these 18-gauge jump rings with a 4.5mm I.D. (inner diameter) and 6.6mm O.D. (outer diameter). This is a great size ring for learning to make box chain, and the large array of vivid colors gives you plenty of options for creativity! Best yet, these jump rings are made in the USA using a combination of copper wire and brilliant enamel coating that is easy to manipulate and hard to scratch. Jump ring sizes follow the American Wire Gauge (AWG) system of measurement, and the inner diameter measurement corresponds to the size of the mandrel on which the jump rings were made.