A tool for opening and/or closing rotatable joints, wherein - it includes a slewing ring, a first grip member, and a second grip member, and - the first grip member consists of an annular plate that has form-locking surfaces to be adapted on a nut of the joint, and - the second grip member consists of two identical gripper arrangements which include a gripper, an actuator, and bearing members of the actuator, and in that the gripper is a plate with the shape of a substantially equilateral triangle which is fastened in a pivoted manner at the centre of gravity of the plate between plates and of the slewing ring by means of a pivot pin, and - the slewing ring consists of an annular upper plate and, placed lower, an annular guide plate, between which plates are adapted grippers of the second grip member, and - the guide plate is adapted to slide in slots of slide pieces which are in connection with the first grip member, and - the slide pieces consist of an upper piece, a centre piece, and a lower piece, which pieces are connected to the annular plate of the first grip member by joint members, such as screws, passing through the pieces, and in that the upper piece and the lower piece are of the same size, but the centre piece is smaller than them, thereby creating the slot - the gripper has a cylindrical surface which likewise adapts on the cylindrical surface of the shaft and which has gripper pieces, and - the bearing members of the actuators are in connection with the first grip member, which actuators are adapted to move the grippers of the second grip member, and - the grippers are fastened to the slewing ring in a pivoted manner and adapted to grip the shaft of the joint. - it includes a slewing ring, a first grip member, and a second grip member, and - the first grip member consists of an annular plate that has form-locking surfaces to be adapted on a nut of the joint, and - the second grip member consists of two identical gripper arrangements which include a gripper, an actuator, and bearing members of the actuator, and in that the gripper is a plate with the shape of a substantially equilateral triangle which is fastened in a pivoted manner at the centre of gravity of the plate between plates and of the slewing ring by means of a pivot pin, and - the slewing ring consists of an annular upper plate and, placed lower, an annular guide plate, between which plates are adapted grippers of the second grip member, and - the guide plate is adapted to slide in slots of slide pieces which are in connection with the first grip member, and - the slide pieces consist of an upper piece, a centre piece, and a lower piece, which pieces are connected to the annular plate of the first grip member by joint members, such as screws, passing through the pieces, and in that the upper piece and the lower piece are of the same size, but the centre piece is smaller than them, thereby creating the slot - the gripper has a cylindrical surface which likewise adapts on the cylindrical surface of the shaft and which has gripper pieces, and - the bearing members of the actuators are in connection with the first grip member, which actuators are adapted to move the grippers of the second grip member, and - the grippers are fastened to the slewing ring in a pivoted manner and adapted to grip the shaft of the joint.