by rubber bumpers 35a which are positioned to be contacted by the inner surfaces of the binder leaves 23 and 24 in accordance with the invention a pneumatic or hydraulic cylinder 38 is mounted on front wall member 13 of the shuttle box the cylinder having a piston 39 and a piston rod 40 the piston rod mounting at its distal end a non metallic preferably plastic tip 41 position to contact the binder 22 in the area underlying pivot pin 29 a spring 42 normally biases the piston 39 and piston rod 40 to the retracted position in similar fashion the front wall member 14 mounts a cylinder 43 having a piston 44 and piston rod 45 mounting a non metallic tip 46 the piston and piston rod being normally biased to the retracted position by a spring 47 fluid under pressure is adapted to be introduced into cylinder 38 and relieved therefrom by means of pressure regulating means 48 and a similar pressure regulating means 49 is provided for cylinder 43 the pressure applying cylinders 38 and 43 are preferably of different sizes with the cylinder acting upon the trailing end of the binder being larger thereby permitting a higher degree of loading at the point where the binder pivots however the cylinders may be of the same size and if desired they may be jointly activated and deactivated by a single pressure regulating means however independent control of the cylinders is preferred thereby providing greater flexibility in adjustment in the operation of the shuttle box it is desirable.