Horizontal Struts
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.
Automatic Door Opener
One of the greatest inventions of all time! Okay, maybe not the greatest, but they sure are nice to have, though a significant pain if they are not working correctly. When all the other components of a door are working correctly, the opener smoothly and effortlessly opens and closes your overhead door by the simple push of a button. The most popular designs of door openers are chain drives and screw drives. Each has its advantages and disadvantages.
Door Panel Hinges
Almost all modern overhead doors are built using multiple horizontal panels. These panels need to be connected somehow, and because the door needs to follow the tracks when opening and closing, it needs to hinge where the panels meet. That is what the hinges take care of. It may sound simple, but just like any other moving part, hinges can wear out too.