The Mending Wheel or Wheel of Mending is one of the artifacts Tiberius was looking for and eventually found before the campaign started streaming on Twitch as Critical Role. It allows the user to magically repair damaged items and gems.
Tiberius acquired the wheel when he and the party fell into an ancient cistern within Emon and were attempting to find their way out. They ended up discovering the ruins of a city where a hag was living. In exchange for a part of Tiberius's luck, she traded him the wheel. She showed them the way out and back to the surface after they slayed an umber hulk, in an encounter where Grog almost died.