LiftMaster 71-1550B18LGH 18-Tooth #50 Chain Sprocket Kit – 1-Inch Bore

The LiftMaster 71-1550B18LGH is a 50B18 sprocket kit for a compatible chain-driven operator installation. It combines an 18-tooth #50-chain sprocket with a 1-inch bore and a 1/4-inch key specification. Use the exact part number and required drivetrain dimensions when selecting a replacement. This is a mechanical service component for a correctly matched shaft and chain path. The bore, keyed connection, tooth count and mounting geometry all matter, so compare the original assembly before treating another sprocket with similar headline dimensions as an equivalent.

Compatibility — Models, Versions and Exclusions

A Matching Tooth Count Is Only the Beginning

This part must fit both the shaft and the chain path. A mechanically plausible fit can still be wrong if the hub position moves the sprocket out of alignment, the key does not engage correctly or there is insufficient clearance. Compare the original assembly and the equipment drawing before treating another 50B18 sprocket as an equivalent.

Describe the replacement as a drivetrain repair, not a speed upgrade. Changing tooth count changes the drive relationship and may affect the equipment’s operation. A worn sprocket should also prompt inspection of the chain, mating sprocket, shaft and keyway so that damage elsewhere is not overlooked. The appropriate repair depends on the complete assembly, not only this one component.

Specifications

How to Choose the Correct Sprocket

Check the chain size, tooth count, shaft diameter, key dimensions and mounting arrangement together. A sprocket with the right bore but a different tooth count changes the drive relationship. A similar-looking sprocket for another chain size is not an equivalent replacement.

• Match the operator or installation parts list to 71-1550B18LGH.
• Confirm a 1-inch shaft fit and the specified keyed connection.
• Compare sprocket alignment and clearance with the original installation.
• Have worn chain and mating sprockets assessed during replacement.

Frequently Asked Questions

Will a 1-1/4-inch bore version fit the same shaft?

It is a different bore configuration. Order the version specified for the actual shaft and approved installation.

Does this kit include a complete chain drive?

This item is identified as a sprocket kit. Confirm any required chain, shaft, keys or additional mounting hardware separately.

Safety Warnings — Read Before Installation or Service

• WARNING: Exposed chains, sprockets and shafts can catch clothing or fingers and cause serious injury. Never inspect or adjust them while powered equipment can move.
• Disconnect and secure operator power, including backup supplies, and secure the door or gate before drivetrain work.
• Do not loosen or disturb a door’s spring or counterbalance system as part of an unqualified sprocket replacement.
• Have the technician verify alignment, retention and chain condition, restore guards, and complete the operator’s required operational and safety checks.

Related Products and Important Differences

• 50B18 sprocket — 18 teeth, #50 chain, 1-inch bore — a dimensional comparison listing. Matching headline dimensions do not establish the same manufacturer kit, hub geometry or hardware package.
• 18-tooth #41-chain sprocket — a different chain family. It illustrates why matching the bore and tooth count is not enough; it is not the #50-chain substitute.

More Questions Before Ordering

Is any 50B18 sprocket the same as this LiftMaster kit?

Not automatically. Verify the full dimensions, hub configuration, material requirements and supplied hardware, along with the equipment manufacturer’s replacement specification.

Can I reuse the old key and set screw?

Have the technician inspect the shaft connection and use the hardware specified for the replacement. The condition of the old components cannot be established from the product number.

Need Help Confirming the Right Part?

Contact Garage-DoorParts.com before ordering. Send the full operator model, readable part labels and photographs of the installed assembly. Include dimensions or the control-box model where relevant. We can help compare the listing with the information you provide; final installation suitability should be confirmed by the servicing technician.