Jimmy and Welding Robot X-5 ‘Bert’ were once the best sanitary engineers in the entire solar system. Jimmy’s bionic rivet gun, worn on his arm, was capable of punching rivets through reinforced Tritanium, but the gun was damaged. They were forced to take menial work as snag-finders aboard construction projects like Space Station Alpha to fund the repairs that were needed.
Fortunately for Jimmy, the Doctor repaired his rivet gun when it was needed to expel a cobalt bomb (of the Klytode’s design) into space before it could explode and crash the space station, changing the Earth's climate. (DWA: The Snag Finders)