Replacement Black U Rings for all CB X chastity devices, these U-Rings are compatible with all models and spare parts. A CB X complete kit includes U Ring sizes  numbers 1 to 5. Needing a U-ring larger than the  number 1 supplied in your kit?

Seven sizes of U Rings are available for CB-X chastity devices.

Number 4 measurement is 41.275mm

Wipe clean with warm water and soap. Do not submerge