LiftMaster K72-33872-1 Limit Switch Shaft and Sprocket Kit
The LiftMaster K72-33872-1 limit switch shaft and sprocket kit is a mechanical service kit for the rotary limit system on select LiftMaster medium-duty commercial door operators. The limit shaft works with the limit nuts, sprocket, bearings, and limit switches so the operator can stop consistently at the fully open and fully closed positions.
When this shaft system wears, breaks, binds, loses hardware, or becomes misadjusted, the operator may overtravel, stop short, lose repeatable limits, or require repeated limit adjustment. The symptom can look electrical because the switches are involved, but the shaft, sprocket, nuts, and bearings are mechanical parts that must turn freely and stay aligned.
This kit is commonly listed for MT, BMT, MJ, MH, and MHS medium-duty logic control applications. It is different from the K72-33872-2 MGJ limit shaft kit and different from the K72-12493 limit switch kit. In many repairs, a technician will inspect the shaft kit and the switch kit together because worn mechanical limit hardware and bad switches can create similar travel problems.
Where This Part Is Commonly Used
Use this kit when the limit shaft, sprocket, bearings, or related hardware are worn or damaged on a compatible medium-duty operator. It is especially relevant when the door runs past limit, loses the open or close stop point, or has a visibly damaged limit shaft assembly.
Limit settings must be adjusted after replacement. The door should be tested through full open and close cycles and safety devices should be verified before the operator is returned to service.
Compatible With
Known and commonly referenced compatibility includes the following where the parts diagram lists K72-33872-1:
- LiftMaster MT medium-duty trolley operators
- LiftMaster BMT medium-duty belt-drive trolley operators
- LiftMaster MJ medium-duty jackshaft operators
- LiftMaster MH medium-duty hoist operators
- LiftMaster MHS medium-duty slow-speed hoist operators
- Medium-duty U-logic operator electrical-box parts diagrams that list K72-33872-1
- Not the MGJ-specific K72-33872-2 shaft kit and not the K72-12493 switch kit
Features and Specifications
| Feature / Specification | Details |
|---|
| Manufacturer | LiftMaster |
| Product Type | Limit switch shaft and sprocket kit |
| Part Number | K72-33872-1 |
| Application | Commercial door operator travel-limit mechanism |
| Compatible Operator Type | Select MT, BMT, MH, MJ and MHS medium-duty operators |
| Included Components | Limit shaft, limit nuts, bearings, sprocket, washers, compression ring, roll pin and e-ring in common kit references |
| Function | Transfers operator movement to the limit switch system |
| Notes | Limit adjustment and safety testing required after replacement |
Also Known As / Related Part Numbers
Related search references include:
- K72-33872-1
- 72-33872-1
- LIF-K72-33872-1
- Limit switch shaft kit
- Limit shaft and sprocket kit
- Limit switch shaft and sprocket for MT BMT MH MJ MHS
- Medium-duty limit shaft kit
Technician Note
Do not replace this kit and leave the old limit settings untouched. The limit system must be mechanically aligned and adjusted after service. If the limit chain, sprocket, or nuts are worn, the switches may test good but the door can still stop in the wrong location.
Before Ordering
- Confirm the operator model is MT, BMT, MJ, MH, MHS, or another diagram-confirmed application.
- Confirm the diagram lists K72-33872-1 and not K72-33872-2.
- Inspect the limit switches and consider whether K72-12493 is also needed.
- Check the limit nuts, sprocket teeth, shaft bearings, and hardware before ordering.
- Plan for limit adjustment and full operational testing after installation.
Professional Advisory
Limit-system work affects door travel and stopping points. A commercial door technician should service the operator, set the limits, test all controls, and confirm monitored entrapment protection is working. Do not bypass limit switches or safety devices.
Product Questions and Answers
What does K72-33872-1 do?
It replaces the limit switch shaft and sprocket hardware used by the operator travel-limit system on select medium-duty LiftMaster commercial door operators.
No. K72-33872-1 is commonly listed for MT, BMT, MH, MJ, and MHS applications. K72-33872-2 is commonly tied to MGJ applications.
Does this kit include the limit switches?
This kit is for the shaft and sprocket assembly. The separate limit switch kit is commonly referenced as K72-12493.
What symptoms can point to a bad limit shaft kit?
Overtravel, inconsistent stopping points, stripped sprocket teeth, loose limit nuts, binding, or repeated limit adjustment can point to worn limit shaft hardware.
Do the limits need to be reset after installing this kit?
Yes. The open and close limits should be adjusted and tested after the shaft kit is replaced.
