A spindle drive unit, in particular for an actuator having a planetary screw drive (PWG) for actuating a clutch of a motor vehicle by an actuating element is provided, where the drive unit has an e-motor with a rotor and a stator and where a spindle provided with a pitch is connected non-rotatingly to the rotor and is drivable by the rotor around an axis of rotation. The spindle is designed as a threaded rod and a rotor carrier that holds the rotor is screwed onto the threaded rod, and the rotor carrier is rotationally secured and axially fixed on the spindle by a lock nut.