 A component of the DLA is a pinion which engages with the race ring that serves as a bull gear.There are two race rings and two DLAs in each SARJ providing on-orbit redundancy, however a series of space walks would be required to reposition the DLAs and the Trundle Bearing Assemblies (TBAs) to utilize the alternate race ring.A spare DLA was brought to the ISS on STS-122.