The company that makes these specializes in making captives bead rings from premium materials! The quality is amazing and the polish is mirror finish.
The below measurements are approximate: 18g and 16g: 1/4" thru 7/16" diameter captives have 3mm beads 1/2" and 9/16" diameter captives have 4mm beads
14g and 12g: 1/4" thru 3/8" diameter captives have 3mm beads 7/16" and 9/16" diameter captives have 4mm beads 5/8" and 3/4" diameter captives have 5mm beads 7/8" and 1" diameter captives have 6mm beads