I invented a special trolley hoist,my trolley can travel,not only on an I beam,but square,rectangular,round,and trusses,etc..<br/>Unit is maintence free,can be used on all type vehicles,also rescue operations, warehouse,sea going ships,etc..<br/><br/>No need for a forklife,powergait,or docking ramp.<br/>Trolley has rollers on top,and bottom of beam,with steel plates on top,and bottom.<br/>has a sleave,with one or more booms,extends out past end of beam travel,and retracts to trolley,then trolley moves back to begining of vehicle,doesen't extend past end of vehicle.