Abstract: The invention relates to a device for the rotary assembly of a member controlled by pressurized fluid, comprising a body presenting first and second shoulders opposite which are disposed first and second shoulders, with which is provided the member comprising an inner pipe opening into a groove disposed between this member and the body into which a main conduit, made in the body, opens out, while an inner conduit, made in the body, opens into the first shoulder of the body and is connected to the conduit, the pressure of the fluid contained in the conduit being capable of having such a value that the resultant thrust which is exerted on the first shoulder of the member has for its effect to cause the second shoulders to abut firmly on one another, effecting the locking of elements. One application of the invention is the production of a drag bucket with monitored rotation.