Approximately 29x9.4x3mm copper plated base metal hinged donut bails for jewelry making. These bails have a 16mm inner diameter, and are easy to open and close. Plated over zinc. Copper-plated components tend to be more durable than solid copper parts. Fits up to 3.2-3.6mm chain or cording. For use with 40mm round gemstone donuts up to 6mm thick. Once the interlocking loops are strung onto chain or cording, the donut is securely locked.