Heavy Duty & Thickwall Keensert® Style Threaded Inserts - Locking and Non-Locking

Inch Series KNH, KNHL & Mil-Spec Series MS51831, NAS1395

What is a Heavy Duty & Thickwall Keensert® Style Key-Locking Insert (MS51831 & NAS1395)?

The Heavy Duty & Thickwall key-locking insert (also known in the industry as Keensert®, Keysert, key locking threaded insert, key locking insert, and keylocking insert), in inch/imperial and Mil-Spec sizes, is a threaded insert designed for demanding applications that require enhanced thread strength, durability, security, and reliability. This insert is built from high-quality materials — including 303 Stainless Steel, Nitronic 60, 4140 Alloy, Carbon Steel, and more — to withstand high stress, heavy loads, and severe vibration, making it ideal for lasting and performing well in various environments and in critical thread repair projects.

Available in both locking and non-locking styles (KNH & KNHL), with thread sizes ranging from 4-40 to 1-1/2-12, it is compliant with military specifications such as MS51831 and NAS1395, ensuring it meets the highest standards established by the US Department of Defense (DoD) and the Aerospace Industries Association (AIA) for quality and performance.

Keensert® Style Key-Locking Inserts Heavy Duty, Thickwall, MS51831 & NAS1395 Series at MF Supply

Choose from the Heavy Duty & Thickwall Keensert® style key-locking inserts available below to see available inch and Mil-Spec sizes. Standard materials offered include Stainless Steel, A286, Nitronic 60, 4140 Alloy and Carbon Steel. Standard sizes run from 4-40 through 1-1/2-12.

MF Supply is a leading supplier of Heavy Duty & Thickwall Keensert® style key-locking inserts (MS51831 & NAS1395) in inch & Mil-Spec sizes, including major brands and equivalents to Acme, Alcoa, Camloc, Clarendon, Fairchild, Kaynar, Microdot, Tridair Keenserts®, Chrislynn, McMaster-Carr, Carr-Lane, Jergens, Howmet & Keyserts. Where applicable, our products are DFAR compliant with COC and full certifications available upon request.

Keensert® Style Key-Locking Inserts Heavy Duty, Thickwall, MS51831 & NAS1395 Materials Available

Our Keenserts® style key-locking inserts catalog of Heavy Duty & Thickwall series includes MS51831, NAS1395, MS51831CA, NAS1395CA, MS51831A, NAS1395A, KNH, KNHL, KNH-F, KNH-T, and KNH-MX. They come in Locking and Non-Locking styles and are available in various inch/imperial & Mil-Spec sizes, and in the materials outlined below.

KNH, KNHL, MS51831, and NAS1395 Series – Stainless Steel

The KNHM, KNHML, MS51831, and NAS1395 series Heavy Duty & Thickwall Keensert® style key-locking inserts, made from high-grade 303 stainless steel, are designed to deliver exceptional corrosion resistance and mechanical reliability in demanding environments. Engineered for use in marine, aerospace, and high-humidity industrial applications, these threaded inserts maintain thread integrity under exposure to moisture, salt spray, and corrosive agents. Their high tensile strength and resistance to thread wear make them a preferred choice for structural fastening in environments where component longevity and joint stability are critical. They are available in inch and Mil-Spec thread sizes ranging from 4-40 to 1-12.

• Heavy Duty & Thickwall Keensert® – KNH, KNHL, MS51831 & NAS1395 – Stainless Steel

KNH-F Series – Carbon Steel

The KNH-F series Heavy Duty & Thickwall Keensert® style key-locking inserts, made from carbon steel (also known as black-phosphate steel), delivers exceptional mechanical strength and cost efficiency for high-load industrial applications. The carbon steel composition provides a high tensile strength-to-cost ratio, ideal for applications in construction, automotive, and heavy machinery sectors requiring robust fastening solutions. Designed to withstand significant shear and torque forces, these key-locking inserts ensure thread integrity under dynamic stress. They are available in inch and Mil-Spec thread sizes ranging from 8-32 to 1-1/2-16.

• Heavy Duty & Thickwall Keensert® – KNH-F – Carbon Steel

KNH-T, MS51831CA, and NAS1395CA Series – A286 Stainless Steel

The KNH-T, MS51831CA and NAS1395CA series Heavy Duty & Thickwall Keensert® style key-locking inserts, manufactured from A286 stainless steel, are optimized for high-temperature and corrosive environments. A286’s precipitation-hardened alloy composition provides elevated yield strength (up to 130 ksi) and thermal stability (up to 1300°F), making it critical for aerospace and defense applications such as turbine engines and exhaust systems. These inserts ensure secure, vibration-resistant threading in environments where thermal and mechanical loads exceed the capabilities of standard stainless steel. They are offered in inch and Mil-Spec thread sizes ranging from 8-32 to 1-12.

• Heavy Duty & Thickwall Keensert® – KNH-T, MS51831CA & NAS1395CA – A286

KNH-MX, MS51831A, and NAS1395A Series – 4140 Alloy Steel

The KNH-MX, MS51831A, and NAS1395A series Heavy Duty & Thickwall Keensert® style key-locking inserts, crafted from 4140 alloy steel, are engineered for maximum durability and load-bearing capacity in high-stress applications. The 4140 alloy, with a tensile strength of approximately 140 ksi and enhanced fatigue resistance, is ideal for heavy machinery, aerospace components, and industrial equipment subjected to continuous mechanical stress. These inserts provide great thread strength and impact resistance, ensuring long-term reliability. They are available in inch and Mil-Spec thread sizes from 8-32 to 1-12.

• Heavy Duty & Thickwall Keensert® – KNH-XM, MS51831A & NAS1395A – 4140 Alloy

KNH & KNHL Series – Nitronic 60

The KNH and KNHL series Heavy Duty & Thickwall Keensert® style key-locking inserts, forged from Nitronic 60 stainless steel, are designed for exceptional galling resistance, wear endurance, and corrosion protection in harsh industrial environments. Nitronic 60’s high yield strength and resistance to chloride pitting make it ideal for chemical processing, marine, and petrochemical applications. These inserts maintain thread integrity under abrasive conditions and high-friction interfaces, enhancing component longevity. They are available in inch and Mil-Spec thread sizes ranging from 8-32 to 1-12.

• Heavy Duty & Thickwall Keensert® – KNH & KNHL – Nitronic 60

Cross-reference tables' links:

• Keensert® Cross Reference - Inch & Mil-Spec | MF Supply

Resources:

• Buyer's Guide to One and Done Keensert® Ordering
• Keenserts® Data Sheet
• Keensert® Functional Equivalent Case Study
• Case Study: Smart Manufacturers use Brand Equivalents to Save Time and Money
• Keenserts® vs Helical Inserts: What’s The Difference?
• Keensert® Style Key Locking Inserts Frequently Asked Questions

Why Buy Heavy Duty & Thickwall Keensert® Style Key-Locking Inserts (MS51831 & NAS1395) from MF Supply?

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

We stock a huge inventory of Keensert® style key-locking inserts Heavy Duty & Thickwall, MS51831 & NAS1395 series in inch/imperial and Mil-Spec sizes. Standard materials offered include 303 Stainless Steel, A286, Nitronic 60, 4140 Alloy and Carbon Steel (Black-Phosphate Steel). Standard sizes run from 4-40 through 1-1/2-12.

Additional Inch & Mil-Spec key-locking insert product lines include Miniature & Thinwall, Solid, Extra Heavy Duty, installation tools and kits. Special materials and nonstandard sizes may be available for special orders with a lead time.

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!