Ring

A ring was an item of jewellery which was placed on a finger.

Rings could be used as bio-dampers. The Tenth Doctor gave Donna a bio-damper in the form of a ring so that she would be hidden from the Racnoss. (TV: The Runaway Bride) Gavin wore a bio-damper ring he inherited from his father which hid his alien origins. (TV: The Empty Planet)