LiftMaster K84-SH-76 Castle Hex Nut — 3/4-16

The LiftMaster K84-SH-76 identifies the 3/4-16 hex-nut service reference used in documented commercial-door operator drive arrangements. The supplied record describes it as a castle hex nut. Match the exact nut form, thread and prescribed retention arrangement before ordering; the 3/4-inch thread designation should not be confused with the wrench size or treated as proof that every nut of that nominal diameter is equivalent. 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

Inspect the shaft threads, nut location and adjoining components before choosing a hardware-only repair. A worn or damaged thread can prevent reliable retention even when the replacement nut is correct. Identify the exact service arrangement rather than substitute a common nut on the basis of diameter alone.

The manufacturer drawings separately identify retaining hardware around the clutch assembly. Confirm any required cotter pin or other securing component and the current supplied quantity; an adjacent item in the drawing is not automatically included. Follow the approved assembly and adjustment procedure without guessing a torque or using nut tightening to compensate for worn clutch parts. Verify the affected drive and protection functions after service.

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

• Record the complete equipment model, serial information and installed service reference.
• Match K84-SH-76 in the actual service drawing.
• Verify 3/4-16 and the shaft thread condition.
• Confirm the actual nut geometry and required pin arrangement.
• Confirm the current supplied inventory and the exact installation and final testing instructions.

Package Contents and Separate Requirements

This offer identifies the nut service item. Confirm current quantity and nut form. A cotter pin, washer, shaft, clutch spring, complete clutch assembly and operator are not established as included. Obtain separately required retention hardware from the exact operator service information before arranging the repair.

Safety Warnings — Read Before Installation or Service

• WARNING: A moving commercial door and exposed castle hex nut — 3/4-16 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

Does 3/4-16 describe wrench size?

No. It identifies the nominal thread diameter and threads per inch.

Is a cotter pin included?

No pin is established as included. Confirm the prescribed retention arrangement and separate hardware.

Can it repair damaged shaft threads?

No. Inspect and correct the shaft condition before installing the nut.

Can a generic nut be substituted?

No general substitution is established. Thread, form, retention and approved application must match.

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.