first cone shaped section 20 a of the bore 20 so that when the spreading screw 22 has been screwed in its cone shaped head 22 a lies with its circumferential surface essentially in contact with the inner surface of the first cone shaped section 20 a of the bore 20 as shown in fig2 into the opposite second cone shaped section 20 b of the bore 20 is inserted a spreading nut 24 that displays a bore with an inner thread into which the threaded shaft 22 b of the spreading screw 22 is screwed as can likewise be seen in fig2 in the same manner as the cone shaped screw head 22 a the cone shaped spreading nut 24 is adapted in its outer shape to the second cone shaped section 20 b of the bore 20 so that after its insertion into the bore 20 the spreading nut 24 lies with its circumferential surface essentially in contact with the inner surface of the second cone shaped section 20 b of the bore 20 in the longitudinal direction the cone shaped screw head 22 a and the cone shaped spreading nut 24 are dimensioned in such a way that when the spreading screw 22 and the spreading nut 24 have been inserted into the bore 20 neither the screw head 22 a nor the spreading nut 24 projects beyond the respective faces of the central section 10 of the male part 6 as shown in fig2 and in addition a space still remains between the screw head 22 a and the spreading nut 24 so that for tightening the arrangement.