Different embodiments of hydraulic nut are described comprising a pressure system with screws that may be displaced to an end detent, and once the travel of the screw has finished, there is no possibility of a further forward movement thereof, so there cannot be a hydraulic fluid leakage. The hydraulic wrench of the present invention may be used in a preventive way, since the nut may indicate a decrease or increase in the preset stress to which it must operate, or it may indicate that the stress at which it must be installed has been reached. For example, the nut may comprise a visual alarm device, an acoustic alarm device or it may issue a warning signal through phototransistors or radiofrequency.