These rigid struts act as braces to help support your door panels when your door is in the open position. Sometimes you can get by with not installing these on smaller doors, but they are necessary (sometimes required by local building codes) on larger doors. When your overhead door is in the opened position, it is only supported on the ends by the rollers in the tracks. These struts help support the weight of the panels in the middle where there otherwise would be no support. If your overhead door is jerky when it is opening or closing, this could be a result of improperly installed (or MISSING!) struts.