The heading of this particular ring is made of 5 small rectangular frames that are clamped into one another, leaving linear gaps between them, thus making this head partly open, a kind of a filigree.
The heading is laser cut from 4mm birch plywood board. The ring itself is 6mm thick.
The size of the ring itself is selectable, available in 18 sizes from 15.3mm through 22.3mm inner diameter (US 4½ - US 13). The ring simply sticks into the middle of the heading. Sides of the ring is untreated, the outer curved surface is painted to black.
The ring is available at the following marketplaces.