In a hydraulically operated unit, particularly a prop for a support in an underground excavation, a thin-walled tubular jacket is pressed on an inner element which is movable in an outer tubular element so that the tubular jacket has an inner diameter which is determined with a substantial undersizing relative to the outer diameter of the inner element, and the tubular jacket is clamped on the inner element with exceeding of the flow limit of the inner element and only in a plastic expansion condition which exceeds with a reliable distance and elastic deformation region of the tubular jacket and with a sufficient residual springing part.