radial direction as the center hub 20 deflects vertically the radial flexures 60 shorten in the radial direction thereby reducing the compressive load and the negative stiffness effect and increasing the vertical stiffness of the isolator and the vertical natural frequency of the system the softer the elastic structure providing the compressive load the more constant the compressive load as the center hub deflects away from its equilibrium center position and the smaller the increase in vertical stiffness and vertical natural frequency in the present configuration the stiffness of the die spring 56 and the flexures 66 affect the reduction in compressive load as the radial flexures 60 shorten since these elements act in parallel the flexures 66 are very flexible in the radial direction parallel to the radial flexures but very stiff in the horizontal direction perpendicular to the radial flexures this method of support constrains the center hub against deflections in directions perpendicular to the radial flexures 60 two additional thin sheet shear flexures 72 are oriented horizontally and are clamped under the lower radial flexures 60 to the center hub assembly 20 and to blocks 76 with screws 79 the blocks 76 are attached to vertical thin sheet flexures 74 with screws 78 the flexures 74 are attached near their bottom ends to the edge of base plate 22 the shear flexures 72 are stiff in directions parallel to the radial flexures 60 and constrain the center hub 20 from displacements it this direction they are very flexible in bending and with the high flexibility of the flexures 74 in a horizontal direction perpendicular to the shear flexures 72 they add little vertical stiffness to the isolator thus with the system of flexures described that support the radial flexures 60 and connect to the.