of the bolts and the heads 36 of the bolts are smooth circular shanks 34 where a series of parallel plates 38 40 and 42 are translateably mounted as best seen in fig1 plates 38 40 42 have their respective identical tapered edges 44 46 48 inserted between individual coils of the spring 12 each of the plates has a different horizontal dimension as seen in fig1 so that the respective tapered edges protrude different distances into the spaces between the spring coils consequently the respective tapered edges take up varying amounts of the axial distance between individual coils of spring 12 when spring 12 is compressed individual pairs of coils will sequentially sandwich respective plates therebetween and these coils will thereupon be rendered inactive as a result the effective spring rate of spring 12 increases stepwise during its compression the plates may be all of the same thickness but it may be preferable in some instances to use plates not having the same thickness or to use plates whose edges do not have the same degree of taper it may also be preferred that the thickness or axial dimension of each tapered edge vary from its thinnest to its thickest part by more than one half the axial dimension 34 c 34 fig1 of the stock from which the spring is made in this way assuming the plates are translated a sufficient distance away from longitudinal axis 22 of the spring 12 the plates will stack or collapse together after sufficient.