upwardly when the top end of the coil spring 2 is moved to the left and downwardly when the coil spring 2 is rocked to the right the latter situation being illustrated in dotted lines in fig2 based on the knowledge of this mainly vertical maximum displacement of the rod portion c the clamp 10 is designed such that the rod portion c will abut the respective surfaces 12 and 18 when the rod portion c has been displaced approximately half of the vertical maximum displacement by the associated stoppage of the half winding b c from being bent out from b more than corresponding to half the operational vertical maximum displacement the long term weakening of the rod material adjacent the potential breaking area at b will be essentially reduced more than halved because the weakening would otherwise increase exponentially with the oscillation amplitude for high oscillation amplitudes whereby the rod portion c will abut the respective support surfaces 12 and 18 a break action will of course occur at c but since the rod portion c is not directionally fixed the break action will not occur in any concentrated manner at c but will be distributed along the spring rod to both sides of the area or rod portion c i e along the entire length d c b the associated material weakening in each or any of the cross sectional areas of the spring rod along this length therefore will be very small and the result will be a very remarkable prolongation of the lifetime of the coil spring 2.