Strut: A solid one piece of molded sheet metal cut to the same length as the width of your garage door. This reinforcement at the top of your door is there to keep the opener arm that attaches to the top panel of the door from bending top panel when opener pulls on panel to open door. When a door is 10 ft. wide or less than you dont need a strut reinforcement if you do not have an automatic opener attached to it. The strut on doors 10 ft. or less is there to protect the top panel from bending when opener arm pulls on top panel to open the door.

If you do not have a automatic opener

and you have to open it manually than a atrut is not necessary on basic steel garage door. When a garage door is constructed of wood it is even more

necessary to have multiple struts even on smaller garage doors 8-10 ft. wide. If you have a custom carriage door made of all wood or metal panels on the inside and wood overlay on the outside it is also necessary to have sometimes 2 struts on each panel. Steel and wood combination doors really sag a lot when in up position because of the extra weight of the wood on outside.

if the opener malfunctions

deteriorate the trolley or carriage that moves along the screw as it turns. And if the opener malfunctions it can bend the rail out of shape. If this happens the rail will handle this kind of torquing better if the rail is solid compared to a 4 piece rail. If this happens to a Genie screw rail than it pretty much ruins it. They get much louder and effect the travel of the carriage along the rail especially where the screw rails attach to one another. Solid rails are most definitely the best way to go