An actuator assembly for a solar tracking system is disclosed. The actuator assembly includes a gearbox housing and a gearbox cover, a motor, and a lead screw. The gearbox housing and gearbox cover cooperate to define an internal chamber for receiving a gear assembly. The motor is mounted to the gearbox housing and is operatively connected to the gear assembly. The lead screw is operatively attached to the gear assembly and mounted inside an inner tube. A thrust bearing assembly is disposed between the gear assembly and the lead screw, with a portion of a thrust bearing nut being positioned within the thrust bearing assembly. A castle nut engages the thrust bearing nut, with the locking washer being frictionally engaged with the castle nut in an interlocking manner. An inner tube is mounted with in an outer tube for linear movement with respect to the outer tube.