Abstract: A mounting tool for a hydromechanical chuck or mandrel of the type which is clamp connected using a pressure medium in order to clamp connecting a shaft or a shaft tool or a working piece, and in which said shaft or working piece is dismantled from the chuck, and which chuck using a pressure medium in the opposite direction, and which chuck is formed with two separate pressure chambers, a first chamber acting as a clamp connection chamber, and a second chamber acting as a dismantling chamber, which chambers are formed with inlets/outlets provided on opposite sides of the chuck and opening at the periphery thereof.