for any given tensile deflection u03b4 t by changing the lengths of these grooves force versus deflection characteristics represented by curves falling between curve c and the horizontal axis can be obtained in addition to the formation of grooves in the threads the spring holders of fig3 a differ from conventional spring holders in another important respect the rigidity of the thread at the end where the spring engages each spring holder is made sufficiently great to prevent flexing at maximal elongations of the spring this is done by abruptly terminating the threads in cross sectional surfaces 57 59 to provide sufficient thread body at the end to resist flexing alternative means can also be provided for preventing flexing of the ends of the threads for example a radially extending pin can be provided in each spring holder at the end of the thread to reinforce the point where the spring engages the spring holder by reinforcing the ends of the threads the force versus deflection characteristics of the mounted spring is linearized as can be seen in fig6 by comparing curve c for the spring holder assembly of fig3 with curve a for the conventional spring holder assembly of fig1 this linearity demonstrates the resistance of the ends of the threads to flexing both the linearity and the close correspondence of the tensile force p t and compressive force p c for equal deflections was verified by a test of the exemplary spring holder assembly the test results are tabulated in table 1 table 1______________________________________ u03b4 mils p sub t lbs p sub c lbs difference ______________________________________ 0 0 0 50 21 2 21 2.