Decoupler

From Memory Alpha, the free Star Trek reference

A decoupler was a 24th century hand-held tool used for making adjustments to various pieces of technology.

In 2373, Captain Benjamin Sisko spent three hours with a tricorder and a decoupler tweaking the pattern buffers for the replicator systems aboard the USS Defiant in order to keep himself busy while en route to Ajilon Prime. When asked by Jadzia Dax if she could borrow his decoupler to check that he had the replicator buffers properly synchronized, he told her get her own, because he was going to use it to check the sonic shower relays. (DS9: "Nor the Battle to the Strong")