the top of the saddle 87 the saddle 80 is designed with a u shaped groove 85 defined by a u shaped virtual surface that intersects the saddle 80 that extends downward until it terminates at a predetermined distance from the top 87 allowing the placement of a spine stabilizing rod slots 92 and 93 cut parallel to the plane p on the outer surface 89 of the saddle 80 and are used to manipulate the saddle 80 with a surgical tool the bottom section of the saddle 80 provides an inner chamber 81 with a spherical surface with a radius comparable to that of the fastener head 61 underside 63 and said chamber 81 encases the head 61 of the fastener 10 the main defining surfaces of the saddle are shown in fig5 b the fastener 10 in one method as shown in fig6 is inserted at the top 87 tip 14 first and it is moved downward until its head 61 clips through the protrusion 88 by deformation inside the saddle inner chamber 81 the underside 63 diameter of the fastener head 61 is less than the diameter of the inner thread 84 except at the protrusion 88 which retains the screw head 61 into position and prevents any upward movement of the fastener head 61 the fastener threaded body 16 comes out of the circular opening 90 at the bottom of saddle and as such the fastener 10 rotates freely through broad angles with respect to the longitudinal axis d d u2032 of the saddle 80 the bottom of the chamber 81 transitions downward to the circular opening 90 through a short extension 83 that opens at an angle until the bottom 82 is reached once the saddle.