K020B0021-1 20B21-1 Drive Belt for Screw Drive Openers
The LiftMaster K020B0021-1 is a small replacement drive belt used inside select screw drive garage door opener systems. Unlike the long one-piece belt found on belt-drive rail openers, this belt is part of the screw-drive power transfer arrangement. Its pitch and width must match the original pulley system so the opener can transfer motor rotation without slipping or chewing the belt teeth. A worn belt may cause grinding, erratic movement, motor running without rail movement, or visible cracking around the belt teeth. Correct identification matters because LiftMaster, Chamberlain, and Craftsman openers use several belt styles that are not interchangeable by length or appearance.
Compatible With
For use with select LiftMaster, Chamberlain, and Craftsman screw drive garage door openers that specify K020B0021-1, 020B0021-1, or 20B21-1. Manufacturer references describe this as a 5 mm pitch, 10 mm wide replacement belt for various screw drive garage door openers. It should not be confused with long belt-drive rail kits such as 41A5250, 41A5434 series, or other one-piece belt assemblies used on belt-drive trolley openers.
Features and Specifications
| Manufacturer | LiftMaster / Chamberlain Group |
| Product Type | Drive belt |
| Part Number | K020B0021-1 |
| Application | Motor drive belt for select screw drive opener assemblies |
| Compatible Operator Type | Select screw drive residential garage door openers |
| Belt Pitch | 5 mm |
| Belt Width | 10 mm |
| Notes | Not a standard long belt-drive rail belt |
Also Known As / Related Part Numbers
- K020B0021-1
- 020B0021-1
- 20B21-1
- LiftMaster 20B21-1
- LiftMaster K020B0021-1
- Chamberlain K020B0021-1
- Screw drive opener belt
- 5 mm pitch 10 mm wide belt
Technician Note
If the belt failed because the screw rail is binding or the pulley is worn, a new belt may fail again. Inspect the pulley, rail, trolley, and drive system before returning the opener to service.
Before Ordering Checklist
- Verify the original belt number is K020B0021-1, 020B0021-1, or 20B21-1.
- Confirm the opener is a compatible screw drive model.
- Do not order this for a standard belt-drive rail opener.
- Inspect pulley teeth and belt alignment before replacing the belt.
- Check for rail binding or stripped drive parts if the old belt failed suddenly.
Professional Advisory
A broken drive belt can be a symptom, not just a worn part. If the opener is noisy, jammed, or lifting unevenly, correct the mechanical cause before installing the new belt.
Important Ordering Warnings
- Not interchangeable with long 7 ft, 8 ft, or 10 ft belt-drive rail belts.
- Do not force a mismatched belt onto a pulley; incorrect pitch or width can damage the drive system.
Product Questions and Answers
Is K020B0021-1 the same as 20B21-1?
Yes. K020B0021-1 is also commonly listed as 020B0021-1 and 20B21-1.
Is this belt for a standard belt-drive garage door opener?
No. This is a smaller drive belt for select screw drive opener assemblies, not the long rail belt used on standard belt-drive openers.
What are the belt dimensions?
Manufacturer references identify this belt as 5 mm pitch and 10 mm wide.
What symptoms can point to a worn screw-drive belt?
Common signs include slipping, grinding, motor operation without proper rail movement, visible cracking, or stripped belt teeth.
Should I replace other parts with this belt?
Inspect the pulley, rail, trolley, and drive components. If another part is binding or worn, replacing only the belt may not solve the problem.
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