The most intricate and fussy part of any garage door is the garage door opener and its associated nuts, bolts, and hardware. You have to deal with the drive mechanism, the long tracks, the tightly-wound and dangerous springs, the brackets, and more. These all combine to make the garage door open nice and smooth time and time again, no matter how much you use it.
And then you must remember, not all garage door opener parts are created equal- in fact, each brand name and each model has different sizes, shapes, and parts, and some even use completely different mechanisms to operate.
In fact, there are three main category of garage door opener, including chain drive (the most basic, and noisiest), screw drive (slightly quieter but still fairly loud), and rubber belt-drive (the quietest.) These all use similar physics but different specifics to wrench open your door every day.