Abstract: A mechanism for rotating the grab bucket of an excavator is formed with a stator having a shaft extending into the bore of a rotor with hydraulic ducts being provided in the stator and the rotor in flow communication with each other for activating the grab bucket by means of a hydraulic drive mechanism externally connected therewith. The ducts in the stator and the rotor are hydraulically connected by circular passages formed on the outer circumference of the stator shaft and shoulders formed in the rotor and the stator operate to have arranged therebetween bearing means on opposite sides of the circular passages which interconnect the ducts between the stator and the rotor.