A thimble used by Harriet Tubman to stitch rags together to make clothing for her fellow slaves. It is kept in Warehouse 13.
Over the course of Tubman's life, the thimble became imbued with her dream of a better life, and took on the ability to refract light such that the wearer could take on the appearance of any person she or he chooses. It came in handy when she was moving slaves through the underground railroad.
Despite being described as merely capable of refracting light, the thimble also has the ability to change the wearer's voice, and possibly their physical dimensions.
In 2010, Leena used the Thimble to take on the appearance of Claudia Donovan, effectively framing Claudia for breaking James MacPherson out of the Bronze Sector. MacPherson later used the Thimble himself to take on the appearance of a physicist at CERN in order to use Joshua Donovan's access to steal a sample of antimatter. Upon his return to the Warehouse, MacPherson was captured by agent Myka Bering, who used the Thimble to take on the appearance of the newly-freed Helena G. Wells.
In 2012, the thimble was seemingly stolen by Brother Adrian, but was actually taken by Artie Nielsen while under the effects of Ferdinand Magellan's Astrolabe. He used it to take on Adrian's appearance in "Endless Wonder" to trick Claudia, Steve Jinks, and Artie himself.
In "The Greatest Gift", which occurs in an alternate time continuum in which Pete never existed, it is mentioned that the thimble has not yet been found. Pete's first interaction with the warehouse (in the real time continuum) was in "Pilot", which suggests the thimble was found thereafter. Since it is later revealed that Pete's mother, Jane Lattimer, is a long-time regent, however, it's theoretically possible that Pete's existence played a critical role in causing Jane to facilitate the snagging of the thimble.