The tool locker was a section aboard USS Enterprise-D where tools were stored. Deep Space 9's tool locker was located on level three, section five. In 2369, it was identified as an independent tritanium source by DS9's computer. Miles O'Brien ruled it out as a possible location for his missing EJ7 interlock, as he'd searched the locker three times already without finding it. (DS9: "In the Hands of the Prophets")