<p>The apparatus has a support tube (2) surrounding a screw thread end section (A) of a threaded bolt (3). Cylinders (1) are arranged in an extension of the tube and movable in a longitudinal direction (L). Pistons (5) are connectable with a hydraulic supply (6). A pin (20) is movably arranged in the longitudinal direction by the pistons. A pin end (22) of the pin is supportable against an end of the bolt. A detecting unit (30) detects a position of the pin in the longitudinal direction. Evaluation and control units (35A, 35B) are connected with the detecting unit and release the supply.</p>
