LiftMaster 71-1550B72LKH #50 Sprocket — 72 Teeth, 1 inch Bore

The LiftMaster 71-1550B72LKH identifies a #50 roller-chain sprocket with 72 teeth and a 1 inch bore. The ordering specification also identifies a 3/8 inch keyway and two set screws. Match the complete drive arrangement before selecting this commercial-door service part. Select the replacement by the complete part number and the installed equipment configuration. A similar photograph or a shared LiftMaster brand name does not establish interchangeability. Confirm the applicable service drawing before ordering so the repair addresses the correct component and its related mounting, connection and operating requirements.

Compatibility — Models, Versions and Exclusions

Identify the Assembly and Plan the Repair

Sprocket selection affects more than whether a part slides onto a shaft. The 72-tooth count must suit the documented relationship between the operator drive and the door mechanism. Do not choose a different tooth count as an improvised speed or lifting-capacity change. Compare the mating sprocket and chain path with the equipment-specific drawing before ordering.

Inspect the existing #50 chain, shaft, keying and attachment points together. A worn or misaligned chain can damage a replacement sprocket, while a damaged shaft can prevent reliable retention even when the nominal bore is correct. Measure the actual mounting arrangement and obtain the applicable hub and clearance dimensions if the existing part number cannot be read.

Compare the replacement with the installed service arrangement before dismantling the equipment. Photograph the part’s location and record the complete model and visible service numbers. Inspect the surrounding attachment points and mating components for wear, impact damage or misalignment. Replacing one worn item will not correct a damaged support or another component that continues to impose abnormal loads on the repaired assembly.

Specifications and Product Identification

Before Ordering

• Confirm #50 chain and 72 teeth against the approved parts list.
• Check the 1 inch shaft fit and available hub clearance.
• Verify keying, alignment and retention before ordering.
• Determine whether the chain, shaft key or mating sprocket also needs service.

Package Contents and Separate Requirements

This offer identifies the sprocket service reference. Confirm the current carton inventory, including the specified set screws, before planning the installation. Do not assume that a shaft key, roller chain, master link, shaft, mating sprocket or complete drive assembly is included. Dimensions identifying screw threads do not identify the supplied length or every mounting requirement.

Safety Warnings — Read Before Installation or Service

• WARNING: A moving commercial door and exposed #50 sprocket — 72 teeth, 1 inch bore can cause serious injury or death. Have a trained door-systems technician perform installation and service.
• Disconnect mains power and any battery backup before mechanical work or wiring. Secure the door against unexpected movement as directed by its manufacturer.
• Do not work on springs, cables or counterbalance components without appropriate training. Never bypass safety sensors or increase force to overcome binding.
• Restore guards and complete the model-specific travel, reversal and protection-device tests before returning the door to normal operation.

Related Products and Important Differences

• CPS-U monitored photo eyes — separate protection devices for approved commercial-door controls; match the operator and environment.
• TDC12X1BMC MAXUM trolley operator — a complete-operator comparison, not evidence that this legacy service part fits MAXUM.

Frequently Asked Questions

Can I choose a different tooth count for more lifting power?

Use the approved drive ratio. A tooth-count change can affect travel and loading and is not an authorized capacity upgrade.

Does a matching bore prove compatibility?

No. Match the #50 chain, tooth count, keying, hub position and clearances as well as shaft diameter.

Is the shaft key included?

Do not assume so. Confirm the current package contents and obtain the correct key and any other separately required hardware.

Does this include a complete chain drive?

No complete drive is identified here. Inspect the mating chain and sprocket and order other worn components separately when required.

Need Help Confirming the Right Product?

Contact Garage-DoorParts.com before ordering. Send the full equipment model, readable part labels and photographs of the installed assembly. Include the dimensions, electrical configuration or accessory details relevant to your project so the listing can be checked against the actual installation.