US Patent 9248532 Screw tensioning device

The screw tensioning device comprises a support tube (12), a cylinder member (15) and a piston section (17). The piston section serves for moving a tensioning bolt (20) screwed onto the thread of a threaded bolt (31). Provided according to the invention is a depth measuring device (35), which presents an externally visible indication of the screw-in depth (ET) of the threaded bolt (31). This ensures that, when the threaded bolt (31) undergoes extension under strain, there is a threaded engagement with the tensioning bolt (20) along a sufficiently long distance. This avoids the hazard that the screw tensioning device might break off from the threaded bolt.