The spin reversal system was one of the engineering systems aboard Federation starships. It was an integral component of the warp propulsion system.
In this system, which was housed in the antimatter chamber, antiprotons were generated. It was located on deck 42 of Galaxy-class starships.
The location of this system was labeled in a schematic of the secondary hull of the USS Yamato in 2365. (TNG: "Contagion", okudagram)