The present invention concerns a wedge comprising four wedge elements (1, 2, 3, 4). A first wedge element (1) and a second wedge element (2) are arranged moveable towards and away from each other. A third wedge element (3) and a fourth wedge element (4) are placed on opposite sides of the first two wedge elements (1, 2) abutting the two first wedge elements (1, 2) along sloping surfaces. The third and fourth wedge elements (3, 4) will be moved away from each other when the first and second wedge elements (1, 2) are moved toward each other and will be free to move toward each other when the first and second wedge elements (1, 2) are moved away from each other. The movement is accomplished in that a first part (7) is fixed rotatable in the first wedge element (1) and that a second part (6, 40) is fixed non-rotatable in the second wedge element (2). The first and second parts (7, 6, 40) have co-operating threads that are so arranged that the first and second parts (7, 6, 40) will move relative each other when the first part (7) is rotated relative the second part (6, 40).