I make these rings in 1mm (18g) 1.2mm (16g) and 1.6mm (14g) with an inner diameter of 8mm, 10mm, 12mm and 14mm (14g and 16g).
In 18g the ring is a twist open ring where the ornament hangs of the ring. In 14g and 16g the ornament is a captive bead that "clicks" in.
The rings are made of black niobium, a hypoallergenic material that stays black really well. The ornament is handcasted in sterling silver after a prototype that I made. I brush them up to give them a rugged surface before I oxidize them. I then polish off some of the oxide to give them a rustic, antigued look.
You can also choose to have the ornament oxidized black without having the oxide polished off but then you have to be aware that it will wear off with time. It can be re oxidized using Liver of sulphur