MS21044N4 - Military Standard Self Locking Hexagon Aerospace Nut

MS21044N4 – Military Standard Self-Locking Hexagon Aerospace Nut

Available now on the Airparts.aero Marketplace.

Overview

The MS21044N4 is a military-standard, prevailing torque, self-locking hexagon nut, one of the most widely used and essential pieces of hardware in all of aviation. Commonly referred to as a "nyloc" nut, it is engineered to resist loosening under the severe vibration conditions of flight. This nut features a captive nylon locking collar that provides a consistent, reliable locking action. Manufactured from high-strength steel and plated for corrosion resistance, the MS21044N4 is the industry standard for securing bolts and screws in countless non-structural and secondary structural applications.

Key Features

• Nylon Insert Locking Mechanism: The defining feature is an integrated nylon (polyamide) collar at the top of the nut. As a bolt is threaded through, the nylon insert is elastically deformed, creating a powerful, uniform frictional grip on the threads that prevents rotation and loosening.
• Vibration Resistance: The prevailing torque created by the nylon insert makes this nut exceptionally resistant to loosening from high-frequency airframe and engine vibration, eliminating the need for secondary locking devices like cotter pins or lock washers.
• High-Strength Steel Construction: Fabricated from a high-quality carbon steel alloy, providing the tensile strength required to properly preload standard AN bolts.
• Corrosion-Resistant Plating: Plated with a durable cadmium finish per specification QQ-P-416. This protective coating provides excellent resistance to environmental corrosion.
• MS Certified Standard: As a certified Military Standard part, it guarantees the material, dimensions, thread quality, and locking torque performance meet the stringent requirements for use in certified aircraft. It is the superseding part for the legacy AN365-428 nut.

Technical Specifications

• Standard: MS21044 (Nut, Self-Locking, Hexagon, Regular Height, 250°F)
• Full Part Number: MS21044N4
• Legacy Part Number: AN365-428
• Material (N): Carbon Steel
• Finish: Cadmium Plated
• Locking Element: Nylon (Polyamide) Insert
• Thread Specification: 1/4-28 UNF-3B
  • Nominal Diameter: 1/4 inch (0.250 inches)
  • Threads Per Inch: 28 (Fine Thread)
• Wrench Size: 7/16 inch
• Maximum Operating Temperature: 250°F (121°C)

Aircraft Compatibility

The MS21044N4 is a universal hardware component used on virtually every aircraft ever built that utilizes standard AN hardware, including all models from Textron Aviation, Piper, Cirrus, Bombardier, and countless others.

• Common Applications:
  • Airframe Assembly: Securing inspection panels, fairings, and secondary structural components.
  • Systems Installation: Mounting instruments, avionics trays, line clamps (adel clamps), brackets, and other system hardware.
  • Firewall Forward: Used in cooler areas of the engine compartment for securing accessories and baffles, provided temperatures do not exceed 250°F.

Applications

The MS21044N4 is the go-to fastener for creating secure, vibration-proof bolted joints:

• General-Purpose Fastening: The workhorse locknut for the vast majority of non-structural and secondary structural joints in an aircraft.
• Serviceable Joints: Allows for fasteners to be removed and reinstalled for maintenance while still providing a reliable locking action upon re-torquing (subject to inspection).

Why Choose MS21044N4?

A fastener that has loosened due to vibration can lead to component failure. The MS21044N4 provides a simple, lightweight, and highly effective solution to this problem. Using a genuine MS-standard nut ensures that the part has the certified material strength, thread quality, and, most importantly, the correct prevailing torque characteristics to function as a reliable locking device. Substituting with non-certified commercial-grade locknuts is strictly prohibited in aviation as they lack the rigorous quality control and traceability required for flight-critical applications.

Order Your MS21044N4 Nuts Now

Stock your shop with the most common and reliable flight-certified locknut in the industry. Visit Airparts.aero to order your MS21044N4 self-locking nuts today.

The MS21044N4 self-locking nut functions by creating "prevailing torque." This is a measured resistance to rotation that exists even when the nut is not seated against a surface. The locking action is created as the male threads of the bolt engage the smaller-diameter nylon ring, which elastically deforms and creates a 360-degree frictional grip. This constant pressure on the threads prevents the nut from moving relative to the bolt, even when subjected to intense vibration. The 250°F temperature limit is critical; above this temperature, the nylon insert will soften, lose its elasticity, and its locking ability will be significantly reduced or eliminated. For applications exceeding this temperature, an all-metal high-temperature locknut (such as the NAS1805 series) must be used.

Note: This is a flight-critical component. It must be tightened using a calibrated torque wrench to the value specified in the applicable maintenance manual. While reusable, the nut must be discarded if it can be run down to the seating surface by hand, as this indicates the nylon locking element has lost its effectiveness.

Product Overview: 

A nut having a flat bottom and 6 sides. An integral feature is incorporated for locking on the threads of a mating member.

MS21044N4 Part Specifications: 

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