wheel the eccentric shafts 12 form central thrust crank mechanisms with the clamping jaw connecting rod sections 14 and with clamping jaw guide pieces 19 thus when the socket screwing head is stationary these thrust crank mechanisms driving the individual clamping jaws 21a c radially can be moved to and fro since the torque transmission is directed via the drive wheels 13 of the eccentric shafts the clamping force is dependent on the torque exerted on the socket screwing head that is to say on the screwing torque the magnitude of the clamping force is determined by the crank angle of the above mentioned thrust crank mechanism consisting of the eccentric shaft the clamping jaw connecting rod sections and the jaw guidepiece and by the drive torque the clamping force can theoretically be infinitely high when a connecting rod section 14 of the thrust crank mechanism is brought into the covering or extended position during clamping the effective length of each composite connecting rod 14 15 can be varied as a result of rotation on the threaded thrust piece or connecting rod section 15 because of this adjustability the clamping jaws can be matched continuously to the socket diameter furthermore during clamping the crank angle on the thrust crank mechanism can be adjusted as desired by means of the threaded thrust piece.