Time Ring

Time Rings were small time travel devices created by the Time Lords. The first Time Rings were worn on one's wrist, and later ones were worn on one's finger.

The Master duplicated a stolen Time Ring prototype in a plan to send his agents to assassinate key figures in Earth's history, but was thwarted by James Stevens, who used one of the Time Rings to prevent Lee Harvey Oswald's death, and later to assassinate John F. Kennedy. (MA: Who Killed Kennedy)

The Time Lords gave the Doctor a Time Ring to see if all of the victims of the War Lords were restored to their proper places in time and space. (PDA: Players, PDA: World Game)

The Time Lords gave the Fourth Doctor a Time Ring to be used to return to Nerva Beacon after carrying out a mission to prevent the creation of the Daleks. (DW: Genesis of the Daleks) The temporal distortion caused by the Doctor's actions on Skaro disrupted the Time Ring, scattering the Doctor and his companions across the Adelphine Cluster. After peace was established in the region, the Time Lords gave the Doctor a new Time Ring. (MA: A Device of Death) When the Doctor and his companions finally returned to Nerva Beacon, the Time Ring disappeared. (DW: Revenge of the Cybermen)

The Seventh Doctor was given time rings by Muldwych to give to Bernice Summerfield and Jason Kane for their wedding. (NA: Happy Endings)

During the invasion of Gallifrey by the Knights of Velyshaa, all Time Capsules and Time Rings were rendered useless. (BFA: The Sirens of Time)

The Tenth Doctor was forced to give an old Time Ring he found in his TARDIS to a Dalek in exchange for it sparing Earth. Kate Yates set it to self-destruct, destroying the Dalek. (NSA: I am a Dalek)

A Time Ring was used by Harmonious 14 Zink to travel though time 'righting wrongs' as he and his wife went, this time ring was then used during and after the events on Erratoon by Zink and Zara to aide in her search for the Key to Time. (CC: The Prisoner's Dilemma) After Zink was killed by an Ice Warrior on Mars, Zara used it to travel to Safeplace (BFA: The Key 2 Time - The Judgement of Isskar), and then when she was a passenger on the Eschaton and during the conflict between the White Guardian and the Black Guardian on the Planet Chaos. (BFA: The Key 2 Time - The Chaos Pool)