of the retaining wall 108 is preferably slightly wider than the diameter of the undeflected belleville washer 130 such that the loading thereof can result in an unrestrained radial deflection of the washer 130 fig5 b shows a top view of the lower plate 200 of fig3 b referring also to fig6 which shows the fully assembled preferred embodiment of the present invention is shown the radially grooved belleville washer 130 is placed with its wide end against the top plate 100 within the annular retaining wall 108 as shown in fig5 b the annular retaining ring 109 is provided to hold the belleville washer 130 against the internal face 103 of the upper plate 100 within the retaining wall 108 the post 201 of the lower plate 200 is fitted into the central opening 132 of the belleville washer 130 the deflectability of the ball shaped head 207 of the post 201 prior to the insertion of the set screw 205 permits the head 207 to be inserted into the interior volume 233 at the center of the belleville washer 130 subsequent introduction of the set screw 205 into the axial bore 209 of the post 201 eliminates the deflectability of the head 207 so that the washer 130 cannot be readily removed.