the present invention provides a self - propelled impact boring tool which , according to one aspect of the invention , has a simplified tail assembly so that the tool can be readily assembled and dissambled to allow replacement of worn parts . such a tail assembly includes a nut and an end cap which can be secured together by a series of conventional bolts which extend into threaded holes in the nut . the nut , which is screwed into the rear end of the tool body , can be clamped in position with the screws with far less torque than would otherwise be required with a conventional , unitary tailpiece .