by a radius having its origin at each of the foci 72 with the length of the radius being substantially equivalent to the radius of the shank of the bolt 56 the annular rib 66 is trapezoidal in cross section having two lateral faces 76 and a top face 78 the lateral faces 76 each have an angle of inclination 80 relative to the surface of the alignment plate of approximately 16 u00b0 referring now to fig5 through 7 it can be seen that the alignment block 62 is essentially a disk having an outer circumference substantially the same as that of the alignment plate 60 an annular groove 82 is disposed in one surface of the alignment block 62 in cross section see fig7 the groove 82 is substantially trapezoidal having roughly the same shape as the annular rib 66 the groove 82 thus comprises lateral faces 84 and a bottom face 86 the angle of inclination of the lateral faces relative to the surface and the bottom face 86 is approximately 16 u00b0 identical to the angle of inclination 80 a circular aperture 90 extends through the alignment block 62 and is disposed within the circumference of the annular groove 82 the aperture 90 has a longitudinal axis 92 which is offset from the axis extending through the center 93 of the.