Regarding the ring size, we have listed the inner diameter. (We apologize that we were unable to prepare a tool to measure the ring size.) This is a retro ring. ◎ The metal is silver-colored plated. ◎ Inner diameter: Approximately 18mm (According to online research, this seems to be about size 16) The back is made in a way that it might open slightly, allowing for minor adjustments. It is possible to make the size smaller by overlapping the metal parts, but the strength of the metal is unknown. ◎ The metal has peeling plating, scratches, discoloration, and dullness.