Ring Shank with 12mm pad, nickel free antiqued brass. Adjustable. Inside diameter, approx 19mm, before adjustment.

These ring shanks are B-grades as the pads on these ring shanks are just slightly off to one side; doesnt really affect its use.  

Ring shank can be adjusted to fit a larger size, not smaller.

Use epoxy glue for max strength, rough up the surface a little first with fine wet-and-dry sand paper. Two pot epoxy is best, you can get different ones that take different amounts of time to dry, and the longer it takes to dry, the stronger it gets.