MS21042L3 - Bombardier OEM Self-Locking Extended Washer Nut

MS21042L3 – Bombardier OEM High-Temperature Self-Locking Plate Nut

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Overview

The MS21042L3 is a military-specification, self-locking, two-lug, low-profile plate nut, specified by Bombardier Aerospace for use in critical airframe and powerplant applications on their Learjet, Challenger, and Global series aircraft. Commonly called an "anchor nut," this component is designed to be permanently riveted to a structure, creating a fixed, high-strength threaded receptacle in locations where backside access is impossible. The "L" designation is critical, specifying fabrication from A-286 corrosion-resistant steel (CRES), a high-temperature superalloy rated for service up to 450°F. This makes it essential for use in engine compartments, on firewalls, and near hot bleed air systems.

The nut features an all-metal, prevailing torque locking mechanism, created by deforming the upper threads.1 This provides exceptional resistance to loosening under severe vibration and thermal cycling. The nut is silver-plated to prevent galling at high temperatures. For any #10-32 blind-fastening application in a high-temperature zone on a Bombardier aircraft, the certified MS21042L3 is the required engineering solution. 🔥

Key Features

• Genuine Bombardier Aerospace OEM Part: Ensures full conformity to Bombardier's stringent quality and performance standards.

• Mil-Spec Certified: Manufactured and tested in strict accordance with MS21042 (NASM21042).

• A-286 CRES Superalloy Construction: The "L" designation specifies A-286 for exceptional strength and corrosion resistance at high temperatures.

• 450°F Service Rating: Certified for continuous service in high-temperature environments.2

• All-Metal Prevailing Torque Lock: Integral locking feature provides reliable self-locking performance unaffected by temperature or contaminants.3

• Silver Plating for Anti-Galling: Prevents thread seizing between stainless steel components at high temperatures.4

• Two-Lug Base: Provides a stable footprint for riveting and load distribution into the structure.

Technical Specifications

• Part Number / Specification: MS21042L3

• Component Type: Nut, Self-Locking, Plate, Two Lug, Low Height, Fixed

• OEM Designator: Bombardier Aerospace

• Thread Size (-3): #10-32 UNF-3B

• Material / Temp Code (L): A-286 Corrosion-Resistant Steel (CRES), rated for 450°F (232°C).

• Finish: Silver Plated per QQ-S-365.

• Governing Specification: MS21042 / NASM21042.

Aircraft Compatibility

• Bombardier Aerospace: This is a standard mil-spec plate nut used extensively across Bombardier's Learjet, Challenger, and Global business jet families where a high-temperature, #10-32 anchor nut is required by engineering drawings or maintenance manuals.

Note: The correct plate nut for any application must be verified against the specific aircraft Illustrated Parts Catalog (IPC) or Structural Repair Manual (SRM).

Applications

• Engine Nacelles, Pylons & Firewalls: The 450°F rating makes it the standard choice for securing heat shields, access panels, brackets, and clamps in high-temperature zones.

• Bleed Air Ducting Areas: Used for mounting components and securing structure near hot pneumatic system ducting.

• High-Temperature Access Panels: Provides a fixed, reusable thread for securing panels requiring routine removal in hot areas.

Why Choose MS21042L3 (Bombardier OEM)?

Using the correct temperature-rated hardware is critical, especially on high-performance business jets. Substituting a standard, low-temperature alloy steel nut (like an MS21047) in a location specified for the "L" designated MS21042L3 is a catastrophic risk. The heat will destroy the locking feature and potentially compromise the nut's strength, leading to fastener failure. As a genuine Bombardier-specified part, the MS21042L3 guarantees the correct A-286 superalloy, the critical silver plating, and the manufacturing quality needed for safe operation in the demanding environment of a Bombardier jet. ✅

The superior high-temperature performance of the MS21042L3 is a direct result of the metallurgy of its A-286 superalloy construction. A-286 is an austenitic, precipitation-hardenable iron-nickel-chromium alloy.5 Its strength is derived from a specific heat treatment cycle that causes the formation of microscopic, ordered intermetallic precipitates of the gamma prime phase ($$\gamma'$$), primarily $$Ni_3(Al,Ti)$$. These finely dispersed precipitates act as powerful obstacles to dislocation movement within the alloy's crystal lattice, providing exceptional tensile strength and creep resistance at elevated temperatures.6 Simultaneously, the silver plating (per QQ-S-365) acts as a high-temperature solid lubricant.7 Under the extreme pressure of torquing, the soft silver shears and coats the thread surfaces, preventing the microscopic cold-welding (galling) that would otherwise occur between the two stainless alloy surfaces, ensuring the fastener can be properly torqued and later removed without damage.

Note: The MS21042L3 must be installed using two appropriate structural rivets. These are prevailing torque nuts and have limited reusability; check minimum prevailing torque before reuse per the maintenance manual. Installation must be performed by a certified A&P/IA mechanic.

Documentation

• NASM21042 (Standard): The current standard for these plate nuts is a controlled document. However, the legacy MS21042 specification sheet, defining core requirements, is often available via online mil-spec libraries.

• QQ-S-365 (Plating Specification): This standard for silver plating is available through various online specification databases.8