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Inch & Metric Keensert® Style Key Locking Inserts

What is a Keensert®?

A key locking threaded insert, also known by its trademarked name Keensert®, is a solid bushing style insert with both internal and external threads. It has wedges or “keys” on one end that create a mechanical lock upon installation, and provide strong, permanent, metal threads in virtually any material — ferrous, non-ferrous or non-metallic.

Keenserts® are used to repair or reinforce threads across many industries, including aerospace, automotive, and heavy machinery manufacturing and repair. Keenserts® are particularly valuable in heavy wear, high vibration and high heat situations where saving space is not the primary concern and where hole depth is limited. In addition to thread repair and reinforcement applications, Keenserts® are also used in new part manufacture to improve thread durability to a softer parent material.

Keensert® Style Inserts at MF Supply

Choose from the Metric Keylocking Inserts or Inch & Milspec Keylocking Inserts below to see available materials and sizes. Standard materials offered include Stainless Steel, A286, Nitronic 60, 4140 Steel & Carbon Steel.

MF Supply is a leading supplier with an expertise in Keensert® style key locking inserts. We stock and source a large inventory, including major brands and equivalents to Acme, Alcoa, Camloc, Clarendon, Fairchild, Kaynar, Microdot, Recoil, Rexnord and Tridair Keenserts® in imperial, metric and mil-spec sizes and materials.

In addition to major brands and equivalents, our catalog of imperial, metric and Mil-Spec Keenserts® style inserts includes a variety of styles, sizes, materials and finishes, in both self-locking and non-locking styles. We’ve detailed the main available Keensert® styles below.

Keensert® Styles Available

Miniature | KNC

Miniature key locking inserts are used in electronic and aerospace applications where size and strength are critical. These inserts may be installed in sheet material as thin as 1/16″. Sizes available include inch, 2-56 through 1/4, and metric M2 through M4.

Thin Wall | RKKA | KNM

Used when minimal space is available or in applications where less material needs to be removed. They offer a good balance between strength and size. Available off-the-shelf in internal thread 8-32 through 1/2-20, and metric M5 through M12. Often referred to by their original Fairchild part numbers:KN and RKKA.

Heavy Duty | RKK | KNHM

Also called Thick Wall, these key locking inserts are designed for higher strength and durability; suitable for applications subject to high stress or where a stronger thread is required. Available off-the-shelf in internal thread 4-40 through 1-1/2-12, and metric M4 through M24. Often referred to by their original Fairchild part numbers: RKK.

Extra Heavy Duty | KNHXH

These inserts are used in extremely demanding applications where very high pull-out and torque resistance is needed. Available off-the-shelf in internal thread 6-32 through 1-12. No standard metric option available. Often referred to by their original Fairchild part numbers: KNHXH.

Solid | KNJ

Unlike other Keensert® types that have both internal and external thread, solid inserts have only external thread. Once installed, they can be drilled and tapped as required. These solid inserts can be used to relocate misplaced holes, customize the internal threads, or plug existing holes. They are extremely durable but might require more installation space. Available off-the-shelf in external thread 5/16-18 through 1-1/4, and metric M8 through M33. Often referred to by their original Fairchild part numbers: KNJ.

Floating | KNK

Designed to compensate automatically for misalignment from .015 (for 2-56) up to .040 (for #10 and larger sizes). Sizes include 2-56 through 1/2-20. The floater is supplied as a one-piece unit. Ideal for use on curved surfaces or for use with flathead screws.


Self-locking style key locking inserts have a distorted internal thread that creates a mechanical lock, making them some of the strongest inserts available. Not all key locking inserts are available in the self-locking style.

Keensert® Tools

MF Supply offers pneumatic tools, hand tools, broaching tools and drills and taps used in the installation process.

Keensert® Materials Available

Keenserts® are manufactured in carbon steel, alloy steel, stainless steel, A286, 4140 Alloy and Nitronic. Not all materials are available off-the-shelf in all sizes, and carbon steel and stainless steel are the most readily available options. Below we break down the attributes and uses of each material.

Carbon Steel: Strong and wear-resistant, carbon steel inserts offer the best balance of strength and cost-efficiency for general-purpose use where extreme temperatures are not a concern. They are commonly used when the primary concern is strength vs. corrosion resistance.

Stainless Steel: Stainless steel Keenserts® are known for their corrosion resistance, especially in marine and chemical environments.

4140 Alloy Steel: This is a high-carbon alloy steel that provides superior hardness, offering excellent wear resistance and strength.

A286: A286 is an iron-nickel-chromium stainless steel alloy known for its high strength and corrosion resistance at elevated temperatures. A286 can be more expensive and tougher to machine than Stainless Steel. A286 often has long lead times and may not be available off-the-shelf.

Nitronic 60: This material provides excellent galling and wear resistance. It provides exceptional resistance to high temperature oxidation, crevice corrosion and general corrosion, making it well suited to marine and chemical applications. It is superior in environments where these factors are critical.

Inconel: Known for its ability to withstand extreme temperatures and corrosion, Inconel is often used in high-temperature applications.

What are the Features & Benefits of Keenserts®?

Keensert® style key locking inserts provide strong metal threads in weaker parent materials. They offer high strength and reliability, versatility and the installation process can be learned quickly. Here are some of the top features and benefits of this versatile insert.

Feature: Key locking inserts are strong and reliable, and can stand up to demanding wear, high vibration and high heat environments.

Benefit: The pre-assembled self-broaching keys creates a mechanical lock that is stronger than adhesive-based chemical thread-lockers, eliminating the need for secondary locks. Their solid bushing style construction enhances load distribution, ensuring thread integrity and reducing the risk of stripping or pullout in harsh conditions, high heat and under high-torque demands. The solid bushing style configuration guarantees the quality of the internal thread before installation.

Feature: Keensert® style inserts are versatile, and are available in a variety of sizes, wall thicknesses, materials and sizes.

Benefit: Inserts are able to be installed in a variety of parent materials including aluminum, steel, cast iron, and plastics providing strong, permanent, metal threads in virtually any material — ferrous, non-ferrous or non-metallic. Different insert wall thickness configurations are available to suit a variety of application requirements.

Feature: Keenserts® are easy to install.

Benefit: Installation procedures can be learned in minutes, reducing downtime and labor. Key locking inserts are designed for quick insertion into standard pre-tapped holes, using standard drills and taps, alongside a specialized manual or pneumatic installation tools to drive down the keys. Because the solid bushing style insert has standard external and internal threads, it is difficult to cross thread the insert during installation.

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Why Buy Keenserts® from MF Supply?

WIth over 50 years of experience as a supply chain partner to manufacturers, and deep and broad expertise in fasteners and inserts, MF Supply can help with all your fastening and hardware needs.

MF Supply stocks and sources a large inventory of Keensert style insert options including Miniature, Thinwall, Lightweight, Heavy Duty, Extra Heavy Duty, Self-Locking, Non-Locking, Solid and Floating style Keenserts® in a variety of sizes, materials and finishes. Our mil-spec and certified insert products are DFAR compliant with the manufacturers’ Certificate of Conformance, and full physical chemical certifications available upon request.

Can't find what you're looking for? Email us at [email protected] for a custom quote. "We have the right screw for you" is our motto after all!