MS21042-4 - Textron Aviation OEM Self-Locking Extended Washer Head Nut

MS21042-4 – Textron Aviation OEM Two-Lug Anchor Nut (Nylon Lock)

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Overview

The MS21042-4 is a high-quality, self-locking anchor nut, supplied with the full certification and traceability of Textron Aviation as an Original Equipment Manufacturer (OEM) component. This fastener, commonly known as a plate nut, is a cornerstone of modern airframe assembly, designed to provide a permanent, load-bearing 1/4-28 threaded attachment point in blind locations. This specific version is the standard 250°F-rated nut, utilizing a captive nylon insert as its locking element.

As a genuine Textron Aviation part, the MS21042-4 is the factory-specified component for a vast number of installations across their Cessna, Beechcraft, and Hawker fleets. Its two-lug base allows for secure riveting to the airframe structure, and its reliable nylon lock provides excellent resistance to vibration in general airframe applications that are not exposed to high temperatures.

Key Features

• Textron Aviation OEM Certified: Guarantees the part is the factory-approved, fully traceable component for Textron Aviation aircraft, ensuring compliance with the type certificate.

• Nylon Insert Self-Locking: Features a captive nylon collar that grips the bolt threads to create a consistent prevailing torque, providing excellent resistance to loosening from vibration.

• 250°F Temperature Rating: Certified for use in a wide range of general airframe, cabin, and interior applications where temperatures will not exceed 250°F (121°C).

• Two-Lug Plate Design: The integral base is designed to be securely riveted to the airframe, providing exceptional resistance to torque-out and pull-out forces.

• Cadmium-Plated Steel: The nut body is fabricated from high-strength steel and plated with cadmium per QQ-P-416 for durability and superior corrosion resistance.

• Enables Blind Fastening: Allows for the secure attachment of components in closed-box structures, greatly simplifying airframe assembly, maintenance, and repair.

Technical Specifications

• Part Number: MS21042-4

• Component Type: Self-Locking Plate Nut / Anchor Nut (Two-Lug, Low Height, Fixed)

• OEM Authority: Textron Aviation

• Governing Specification: MS21042 / NASM21042

• Material: Steel, Cadmium Plated per QQ-P-416

• Locking Element: Nylon Insert (or equivalent non-metallic, 250°F rated)

• Thread Specification: 1/4-28 UNF-3B

• Maximum Operating Temperature: 250°F (121°C)

• Installation Method: Attaches with two 3/32" rivets (typically AN426AD3 countersunk type).

Aircraft Compatibility

As a Textron Aviation OEM part, this anchor nut is the specified component for a multitude of applications across their entire product line.

• Primary Textron Aviation Platforms:

  • Cessna Citation Series Business Jets

  • Beechcraft King Air, Baron, and Bonanza

  • Cessna Caravan and Piston Aircraft

  • Hawker Business Jets

• General Aerospace Usage: As an MS-standard part, it is a fundamental construction component used on virtually all certified aircraft in ambient temperature locations.

Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the aircraft's Illustrated Parts Catalog (IPC) and maintenance manual to confirm part number eligibility and the correct temperature rating for a specific location.

Applications

• Attaching inspection panels, access doors, and fairings in general airframe locations.

• Securing floor panels, interior components, upholstery, and cabin systems.

• Mounting avionics racks, equipment trays, and instrument panels.

• Attaching brackets and clips to ribs, stringers, and skin in areas not exposed to high temperatures.

Why Choose this MS21042-4?

This component provides the dual assurance of meeting the public MS aerospace standard and the specific endorsement of Textron Aviation. This guarantees the nut's mechanical properties and, critically, ensures the correct 250°F rated nylon locking element is used per the aircraft's design. Using the OEM part eliminates the risk of accidentally installing an incorrect or unapproved part, ensuring the joint is secure and the aircraft remains in a certifiable condition.

The MS21042-4's self-locking feature relies on the engineered properties of its nylon locking collar. This element, typically made from a polyamide like Zytel®, is precision-molded and securely captured in the nut's barrel. Its internal diameter is controllably smaller than the major diameter of the mating 1/4-28 bolt. As the bolt is threaded through, its threads displace the resilient nylon material, which creates a powerful and uniform radial compressive force on the bolt. This elastic deformation results in a consistent frictional torque, known as prevailing torque, that resists the rotational forces of vibration. The nylon provides excellent "memory," allowing it to perform reliably over a limited number of installation and removal cycles while also providing a secondary benefit of sealing the threads against moisture intrusion.

Note: This is a structural hardware component. The 250°F (121°C) temperature limitation must be strictly observed; use in higher temperature areas will lead to failure of the nylon locking element. Installation must be performed by a certified mechanic in strict accordance with the aircraft's Structural Repair Manual (SRM). Correct rivet selection and installation are critical to the strength of the joint. The self-locking feature has a limited reuse life.

Documentation

The base standard for this part is publicly available through the Department of Defense ASSIST database. OEM-specific application and installation data is contained within the Textron Aviation maintenance and structural repair manuals.

• ASSIST Document Summary Page for MS21042: http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=36974