assembly 24 because of friction with the force rod 15 and the wall surface 32 so that the inner end surface 43 of the retainer assembly 24 moves to contact the facing stop surface 44 see fig2 the decreasing annular space between the tapered wall surface 32 and the outer surface 30 of the force rod 15 causes the balls 26 to apply force between the outer surface of the rod 15 and the wall surface 32 of the sleeve member 22 this force can expand the sleeve member 22 in the spacing gap 38 as the force on the force rod 15 increases see fig3 from an initial force stroke location a see fig3 to a force stroke location b where the inner end surface 43 of the ball retainer assembly 24 reaches the facing stop surface 44 of the stop section 12 after the ball retainer assembly 24 reaches the stop section 12 the force rod 15 continues to move with frictional contact with respect to the balls 26 and with a constant sliding friction force while compressing the spring 52 the constant friction force is shown by the curve c in fig3 while the curve d shows the sum of constant friction force and the compression force on the return spring 52 this constant sliding friction force and the spring compression dissipates the kinetic energy of the moving mass the cup member 56 serves.