MS21042L4 - Textron Aviation OEM Extended Self-Locking Washer Nut

MS21042L4 – Textron Aviation OEM Two-Lug Anchor Nut

Available now on the Airparts.aero Marketplace.

Overview

The MS21042L4 is a high-strength, all-metal, self-locking anchor nut that carries the dual authority of a Military Standard specification and Textron Aviation Original Equipment Manufacturer (OEM) certification. This fastener, commonly known as a plate nut, is a cornerstone of modern airframe assembly. It is designed to be riveted onto a structural member, creating a permanent, load-bearing threaded attachment point, particularly in blind locations where access to the backside is impossible.

Constructed from cadmium-plated steel, the MS21042L4 is engineered with an all-metal locking feature, making it suitable for high-temperature applications up to 450°F (232°C). As a genuine Textron Aviation part, this anchor nut is the factory-specified component for countless installations on Cessna, Beechcraft, and Hawker aircraft, guaranteeing the correct fit, strength, and performance required to maintain the aircraft's type-certified design.

Key Features

• Textron Aviation OEM Certified: Supplied with the full traceability and quality assurance of Textron Aviation, guaranteeing it is the correct part for their fleet.

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

• Enables Blind Fastening: Allows for the secure attachment of components in closed-box structures where a conventional nut and wrench cannot be used.

• High-Temperature, All-Metal Lock: The locking mechanism is mechanically formed in the nut's barrel, providing a reliable prevailing torque that is unaffected by temperatures up to 450°F.

  
  

  
  

• Fixed Nut Element: The threaded portion is integral and fixed within the base, providing a rigid, non-floating attachment for applications that demand precise alignment.

• Governed by Military Standard: Manufactured in strict accordance with MS21042, ensuring the highest level of quality and interchangeability.

Technical Specifications

• Part Number: MS21042L4

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

• OEM Authority: Textron Aviation

• Governing Specification: MS21042 / NASM21042

• Material: Steel (Carbon or Alloy)

• Finish: Cadmium Plate per QQ-P-416

• Thread Specification: 1/4-28 UNF-3B

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

• Locking Principle: Prevailing torque via deformed threads.

• 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.

Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the aircraft's Illustrated Parts Catalog (IPC) and Structural Repair Manual (SRM) to confirm part number eligibility and installation procedure.

Applications

• Airframe: Attaching inspection panels, access doors, fairings, and fillets to ribs, stringers, and skin.

• Interiors: Securing floor panels, cabinetry, and sidewall components.

• Systems & Avionics: Mounting of equipment trays, avionics racks, and component brackets in areas with restricted access.

Why Choose this MS21042L4?

This component provides the dual confidence of a proven military standard and the explicit endorsement of the airframe manufacturer. The MS21042L4 guarantees the high-temperature performance and reliable locking essential for flight safety. Sourcing it as a Textron Aviation OEM part ensures you are installing the exact hardware listed in the aircraft's engineering drawings, eliminating any doubt about its suitability and maintaining the aircraft's certified integrity.

The MS21042L4 anchor nut is a critical enabler of modern stressed-skin and semi-monocoque airframe design. Its primary function is to solve the "blind fastening" challenge inherent in assembling closed structures like wings and fuselages. By riveting the nut plate to the interior of a structural member, it effectively becomes part of the airframe, ready to accept a bolt from the exterior. The all-metal, prevailing torque locking feature is created by crimping the top of the nut's threaded barrel into a precise, non-circular shape. As the bolt is installed, its threads must elastically deform this crimped section, creating a powerful spring-like frictional force that provides exceptional resistance to loosening from vibration and thermal cycling, a critical feature for maintaining joint integrity.

Note: This is a structural hardware component. Its installation is considered a fabrication or repair task and must be performed by a certified mechanic in strict accordance with the aircraft's Structural Repair Manual (SRM) or other approved data. Correct hole preparation, rivet selection, and rivet installation technique are critical to the strength and airworthiness of the joint. The self-locking feature is reusable for a limited number of bolt installation cycles as specified by the manufacturer.

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

Item Specification

 DESCRIPTION

Military Standard Locking Extended Washer Nut Self

• Self-locking, hexagon style
• Dry film lubricant
• Material: Steel
• Finish: Cadmium overall and chromate overall

Applicable Textron Aircraft

• 1900 Airliner
• 1900C Airliner
• 1900D Airliner
• Baron Series B55, E55, 58 or G58
• Beechjet 400/400A
• Caravan or Grand Caravan EX
• Citation CJ1 or CJ1+
• Citation CJ2 or CJ2+
• Citation CJ3 or CJ3+
• Citation CJ4
• Citation III, VI or VII
• Citation Latitude
• Citation Longitude
• Citation M2
• Citation Mustang
• Citation Sovereign or Sovereign+
• Citation V, Ultra, Encore or Encore+
• Citation X
• Citation X+
• Citation XLS, XLS+ or XLS Gen2
• King Air 100
• King Air 350 or 350C FM-1 to FM-35
• King Air 360, 350i or 350C FM-36 & on
• King Air B200, B200T, B200C or B200CT
• King Air B200GT or B200CGT
• King Air C90, C90A, C90GT or E90
• King Air C90GTi Series
• Premier Model 390
• SkyCourier
• Skyhawk
• Skylane
• Stationair

List not comprehensive, may be applicable on other models.

Note: Verify compatibility with your aircraft’s maintenance manual and consult with a certified aviation technician for proper installation