There are three different kinds of garage door openers: 1) Standard chain-drive openers, 2) jackshaft/belt-drive openers, and 3) screw-drive openers.
The chain-drive openers are the most common type of opener, but they are hard to work on.
The screw-drive opens are the easiest to work on, but they are the slowest.
The jackshaft/belt-drive openers are a compromise of easy to work on and fast to operate.