Abstract: An essentially tubular spring housing (FIGS. 5, 6) is formed with longitudinal slits (8d, 8e) into which the support spring blocking structure (1, 10) can be assembled. The support spring blocking structure, in one form (FIGS. 1, 2) is a longitudinal rail retaining a plurality of stacked blocking plates (2) therein, between abutments (3, 4) which are spaced wider than the length of the stack of plates (2) to permit engagement of a spring plate (7) between selected blocking plates, and thus lock the spring plate, and hence the spring, in selected position. In another embodiment (FIGS. 3, 4), the stacked plates (9) are slidable in a holder band or strip (10a). The holders (1a, 10a) are formed with a longitudinal, externally projecting holding hook (5, 11) to permit storing the blocking structure on the spring holder (right side, FIGS. 5, 6) in readily accessible position.