If you need a U-ring for your CB chastity device, then you can purchase an extra one here.
The U-rings are used as a backpiece so that you can lock your chastity device, and it comes in 5 different sizes, so that it fits you best.
U-ring sizes for CB chastity device:
MATERIAL: Transparent plastic.
INTERNAL DIAMETER: 3.8 cm, 4.0 cm, 4.4 cm, 4.8 cm and 5,1 cm, 5.4 cm, 5.7 cm, respectively.
FITS ON: Amongst others, CB-6000, CB-6000s, CB-3000 and The Curve.