u00b0 thread root width rw1 with the new variable use screw root width rw2 which is about 43 larger the absence of a sharp transition into the screw core eliminates the notch sensitivity present in conventional self tapping screw threads fig6 illustrates the reduction of thread forming torque with the new screw the torque arm ta1 for a conventional 60 u00b0 thread is displaced farther from the centerline of the screw and is therefore longer than the torque arm ta2 for the variable use screw this reduction in the length of the torque arm of the variable use screw reduces the rotational torque required to displace the same volume of nut material as the 60 u00b0 thread form making the variable use screw easier to insert fig7 is a diagram of forces showing the variable use screw thread force and stress reduction in the diagram the radial forces fr1 fr2 are the forces that create the boss burst stress the radial force for the variable use screw fr2 is about 54 less than the radial force of the 60 u00b0 thread fr1 for an axial force fa2 of 250 lbs the new screw produced a radial force of only 67 lbs which is in sharp contrast to the 60 u00b0 thread that produced a 144 lb radial force for a 144 lb axial force the 15 degree tip thread flank angle produces favorable conditions when threading the screw into the plastic boss which reduces internal stress the tip thread flank angle of 15 degrees provides higher loading.