I make this ring with 1mm (18g), 1.2mm (16g) or 1.6mm (14g) in black niobium wire in three different sizes: small, medium and large. The small one measures approx . 9,5mm inner diameter, the medium one approx. 11,5mm inner diameter and the large one approx. 14,5mm inner diameter.
The second picture shows all the ring sizes. The rings are made from niobium that's been heated up to become black. The ornament is handcasted in bronze after a prototype that I made, after I get them back from the caster I give them a rough matte finish.