NCIS

Jethro Gibbs's father Jackson Gibbs (played by Ralph Waite ) was a World War II US Army Air Force fighter pilot, as was Mark Harmon's real life father Tom Harmon.

Whenever we see flashbacks featuring young Gibbs, the younger version is played by Mark Harmon's son, Sean.

The hand tools that Mark Harmon uses on the set of NCIS are mostly his own. Those are the tools that he uses in his own personal workshop.