I make these rings in1.2mm (16g) or 1.6mm (14g) both with square and round wire.
Because the square wire require a little more space in the piercing, it's a good idea to buy a 14g if you normally wear a 12g and a 16g if you normally wear a 14g.
The rings are made from pure niobium that I heat up to make it black. The ornament/lock is handcasted in sterling silver after a prototype that I made, oxidized to bring out detail and then polished.
These are also great to be used as earrings for stretched ears.
This is a captive bead style ring. I've made a video showing how to open and close the different styles of rings, you can see the video under "care and sizes".