I make this ring with1mm (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 last picture shows all the ring sizes but with a gold plated bead instead. The model in the second picture is wearing a medium ring in 1.6mm (14g) wire.
The rings are made from pure niobium, then heated up to achieve the black color and afterwards gently polish to give it a matte but still smooth surface. The ornament is handcasted in sterling silver after a prototype that I made, oxidized to bring out detail and then polished.