Key Locking Threaded Inserts (Heavy Duty & Thin Wall)

What Is a Key Locking Threaded Insert?

A key locking threaded insert is a solid, internally and externally threaded fastener used to repair damaged threads or reinforce threaded holes in metal components.

The insert is screwed into a properly drilled and tapped mounting hole. After it is seated, the built-in locking keys are driven down into the parent material. These keys create a positive mechanical lock that helps prevent the insert from rotating or backing out.

Key locking threaded inserts are also commonly called:

• Key locking inserts
• Key inserts
• Thread repair inserts
• Solid key locking inserts
• Keyed threaded inserts
• Locking key inserts
• Keensert-style inserts

They are commonly used when a component requires stronger and more durable internal threads than the parent material alone can provide.

Heavy Duty vs. Thin Wall Key Locking Inserts

Heavy-duty key locking inserts have a thicker wall and larger external thread. They provide greater strength and are generally used in high-load applications where adequate material is available around the installation hole.

Thin-wall key locking inserts have a smaller external thread diameter. They are used where installation space is limited or where increasing the tapped-hole diameter is undesirable.

When choosing between the two styles, consider:

• Available wall thickness
• Internal thread size
• External thread size
• Required pull-out strength
• Parent-material strength
• Edge distance
• Installation-hole diameter
• Applied load and vibration
• Available installation space

The specification charts show the required external thread and drilling depth for each internal thread size.

Inch and Metric Thread Sizes

Key locking threaded inserts are available in standard inch and metric configurations.

Common inch sizes include:

• #8-32 Key Locking Insert
• #10-24 Key Locking Insert
• #10-32 Key Locking Insert
• 1/4-20 Key Locking Insert
• 1/4-28 Key Locking Insert
• 5/16-18 Key Locking Insert
• 5/16-24 Key Locking Insert
• 3/8-16 Key Locking Insert
• 3/8-24 Key Locking Insert
• 7/16-14 Key Locking Insert
• 7/16-20 Key Locking Insert
• 1/2-13 Key Locking Insert
• 1/2-20 Key Locking Insert
• 5/8-11 Key Locking Insert
• 3/4-10 Key Locking Insert
• 7/8-9 Key Locking Insert
• 1-8 Key Locking Insert

Common metric sizes include:

• M4 × 0.7 Key Locking Insert
• M5 × 0.8 Key Locking Insert
• M6 × 1.0 Key Locking Insert
• M8 × 1.25 Key Locking Insert
• M10 × 1.5 Key Locking Insert
• M12 × 1.75 Key Locking Insert
• M14 × 2.0 Key Locking Insert
• M16 × 2.0 Key Locking Insert
• M18 × 1.5 Key Locking Insert
• M20 × 2.5 Key Locking Insert

Fine-pitch options are also available for selected inch and metric sizes. Refer to the charts above for exact internal and external thread combinations.

Materials & Finishes

Key locking threaded inserts are available in steel and stainless steel.

Steel key locking inserts provide strength and economical performance for general industrial machinery, equipment repair and production assemblies. Available finishes include white, yellow or black zinc plating, zinc-nickel plating and nickel plating.

Stainless steel key locking inserts provide corrosion resistance and material compatibility for demanding environments, outdoor equipment and applications exposed to moisture or chemicals.

Material and finish selection should consider:

• Parent material
• Required strength
• Corrosion exposure
• Operating temperature
• Environmental requirements
• Galvanic compatibility
• Production quantity

Custom materials and application-specific finishes may be available depending on the required size and quantity.

Key Locking Inserts for Aluminum

Aluminum is one of the most common parent materials for key locking threaded inserts.

Because aluminum is softer than steel, repeated bolt installation and removal can cause the original aluminum threads to wear, strip or become damaged. Installing a steel or stainless steel key locking insert creates a stronger and more durable internal thread.

Typical aluminum applications include:

• Aluminum castings
• Machine housings
• Gearbox housings
• Engine components
• Fixtures
• Tooling plates
• Aerospace components
• Robotic equipment
• Industrial machinery

Before installation, confirm that the component has sufficient wall thickness and edge distance for the selected insert’s external thread diameter.

How to Install a Key Locking Threaded Insert

Key locking inserts are installed using standard drilling and tapping operations followed by a key-driving step.

General installation procedure:

1. Drill the damaged or prepared hole to the recommended diameter.
2. Countersink the top of the hole if required.
3. Tap the hole using the external thread size shown in the specification chart.
4. Thread the insert into the tapped hole until it is properly seated.
5. Position the installation tool over the insert.
6. Drive the locking keys into the parent material.
7. Verify that the keys are fully seated and the insert remains properly aligned.

The correct drill size, tap size and drilling depth vary by insert size. Always refer to the dimensional chart before preparing the mounting hole.