28 may be obtained by forming the metal of lever arms 22 into the inwardly extending collars 27 shown in fig3 rod 28 is retained in collars 27 by the inner surfaces of rails 14 a longitudinal shaft 30 is fastened to rod 28 at its center as by welding shaft 30 also assists in retaining rod 28 in collar 27 and facilitates the preassembly of link 16 rod 28 and shaft 30 shaft 30 extends from rod 28 through a hole in cross bar 32 mounted in rails 14 cross bar 32 may be flattened as at 34 in the portions surrounding the hole through which shaft 30 extends the ends of cross bar 30 are formed into trunnions 35 for mounting cross bar 32 in rails 14 a compressive load resisting member such as coil spring 36 surrounds shaft 30 between rod 28 and cross bar 32 collar 37 may be mounted on shaft 30 to assist in positioning coil spring 36 the forward end of shaft 30 is threaded and contains nut 38 one side of the flattened portion 34 may serve as a bearing for coil spring 36 while the other side serves as a bearing for nut 38 the position of nut 38 on shaft 30 controls both the position of link 16 with respect to ski 14 and the extension of spring.