MS21044N6 - Hexagon Self-Locking Nut

MS21044N6 – 3/8-24 All-Metal CRES Self-Locking Nut (450°F)

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Overview

The MS21044N6 is a high-reliability, all-metal, self-locking hex nut manufactured to a precise Military Standard for use in the most demanding aerospace applications. This is not a standard nylon-insert locknut; it is an engineered fastener designed for performance in high-temperature and high-vibration environments. Constructed from high-strength Corrosion Resistant Steel (CRES), the MS21044N6 is rated for service up to 450°F (232°C), making it the specified choice for firewall forward, engine, and bleed air system applications.

Its self-locking feature is achieved through a mechanically deformed thread section that provides a strong, consistent prevailing torque. This all-metal lock is impervious to the high temperatures that would degrade or melt the nylon insert of a standard locknut, ensuring the fastener remains secure. For any critical joint where heat and vibration are significant factors, the MS21044N6 provides an essential margin of safety and reliability.

Key Features

• All-Metal Locking Design: Utilizes a deformed thread locking element that provides a consistent prevailing torque, eliminating the need for nylon inserts and their associated temperature limitations.

• High-Temperature Capability: Rated for continuous operation in temperatures up to 450°F (232°C), making it suitable for powerplant and bleed air applications.

• Corrosion Resistant Steel (CRES): Manufactured from high-strength CRES (such as A286 superalloy), providing excellent strength retention at temperature and superior resistance to corrosion.

• Prevailing Torque Lock: The locking mechanism functions independently of clamp load, providing positive resistance to loosening from the moment it is engaged, even if preload is lost.

• Reusable (Limited): Engineered to be installed and removed for a limited number of cycles (typically 15) while still retaining minimum specified prevailing torque.

• Lightweight Design: Manufactured to the MS21044 standard for a lightweight nut, providing high strength with minimal weight penalty.

Technical Specifications

• Part Number: MS21044N6

• Component Type: Self-Locking Hex Nut, All-Metal, Prevailing Torque

• Governing Specification: MS21044 / NASM21044

• Material: Corrosion Resistant Steel (CRES), e.g., A286 alloy

• Finish: Passivated. May also feature silver plating or dry film lubricant for anti-galling and consistent torque.

• Thread Specification: 3/8-24 UNF-3B

• Maximum Operating Temperature: 450°F (232°C)

• Locking Principle: Prevailing torque generated by a mechanically deformed thread section.

Aircraft Compatibility

The MS21044N6 is a standard hardware component used across all sectors of the aerospace industry where high-temperature performance is required. It is not specific to a single aircraft but is a staple in the design of:

• Military Fighter, Bomber, and Transport Aircraft

• Commercial and Regional Airliners

• Business and Corporate Jets

• High-Performance Piston and Turbine General Aviation Aircraft

• Rotorcraft

Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the aircraft or engine Illustrated Parts Catalog (IPC) and maintenance manual to confirm part number eligibility.

Applications

• Powerplant: Engine component mounting, exhaust system attachments, accessory mounts, and brackets.

• Airframe: Firewall forward installations, bleed air ducting clamps and flanges, flight control linkages, and structural joints in high-temperature zones.

• Systems: Hydraulic pump mounts, landing gear components, and any critical bolted joint that requires a reliable locking feature at elevated temperatures.

Why Choose MS21044N6?

This nut's all-metal construction is its most critical safety feature. Using a standard nylon-insert locknut (e.g., an MS21045) in an application that exceeds 250°F will cause the nylon locking element to melt or degrade, completely eliminating its self-locking capability and inevitably leading to fastener loosening and potential catastrophic failure of the joint. The MS21044N6 guarantees a positive, reliable locking action in thermal environments where other locknuts cannot survive, making it an essential component for flight safety.

The MS21044N6 achieves its self-locking function through the principle of prevailing torque, which is induced by the controlled plastic deformation of the nut's upper threads into a non-circular (typically elliptical) cross-section. As the mating bolt thread advances into this locking element, its crests are forced to elastically deflect the nut's threads back towards a circular shape. This action creates a powerful, 360-degree frictional engagement between the flanks of the nut and bolt threads. The choice of a precipitation-strengthened superalloy like A286 CRES is critical for this application. This material allows the nut to be heat-treated to a high strength, yet retain the spring-like characteristics of the locking element without relaxation or loss of temper at service temperatures up to 450°F, ensuring the prevailing torque remains within its specified limits throughout its service life.

Note: This is a flight-critical hardware component. Installation must be performed by a certified mechanic. To ensure correct joint preload, the running torque (prevailing torque) required to turn the nut before seating must be measured with a torque wrench and added to the final dry torque value specified in the maintenance manual. This nut is reusable for a limited number of cycles (e.g., 15 times); the prevailing torque must be re-checked before each reuse to ensure it meets the minimum requirement.

Documentation

The military standard governing this part is publicly available through the Department of Defense ASSIST database.

• ASSIST Document Summary Page for MS21044: http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=36976

Item Specification:

**Cessna Aircraft Model 441 Conquest II Illustrated Parts Catalog [ Click Here ]
See Page 1219, Figure 01, Item 38
See Page 1221, Figure 01, Item 93