The difference between the replacement gear and sprocket kits is the drive type on the opener unit. You have chain, belt and screw drive. The screw drive uses a totally different type of gear system. The chain and belt drive gear kits are almost identical. If your unit has a DC motor than the motor and gear system is all contained together in one part.

As far as the most common gear kits that Liftmaster makes they come two ways. The gear and sprocket assembly comes all put together in one kit. The other is they will just sell the replacement gear itself. This is if you just need to replace the gear and not the whole assembly.

the gear assembly

The other difference in the gear assembly is the sprocket. A chain drive will have a metal sprocket just like the one you would find on a bicycle. The belt drive openers have a plastic notched sprocket. Also other slight differences are in the different models Liftmaster makes. Like a ¾ h.p. motor the gear kits are not interchangeable because of they way they were engineered. The screw holes will be different, or part of the mounting plate is different just because of the way it needs to fit in the unit is different from other models. Now screw drive openers use a totally different drive system sometimes using a small rubber belt to connect the motor to the screw. The Chain and belt drive opener gear kits also include with the worm gear. This is the plastic gear that is shaped like a big screw.

The Motor and the Gear

The motor turns the worm gear and then turns the common gear with teeth. I have changed a thousand of these gear kits sometimes even in the dark. The worm gear is made of a different material than the plastic gear with teeth. I can’t remember ever having to replace the worm gear. They just don’t wear out. The other gears will last around ten years or so depending on how often unit is used.