MS17826-3 - Aerospace Military Standard Durable Self-Locking Hexagon Nut

MS17826-3 – Military Standard 160 KSI Self-Locking Hexagon Nut

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The MS17826-3 is a flight-critical, high-strength, self-locking hexagon nut manufactured in strict accordance with Military Standard MS17826. This fastener is engineered for demanding aerospace applications requiring exceptional tensile strength and a reliable locking feature to resist loosening under severe vibration. It is specifically designed for use with high-strength bolts (typically rated at 160 KSI tensile strength) in critical structural joints throughout the airframe, engine mounts, and landing gear systems.

Fabricated from heat-treated alloy steel and finished with cadmium plating for corrosion resistance, the MS17826-3 achieves its self-locking capability through a precisely deformed thread section at the top of the nut. This prevailing torque feature creates interference with the mating bolt threads, providing resistance to rotation even without clamp load being applied. The integrity of high-stress bolted connections depends on the proven strength and locking performance of certified hardware like the MS17826-3.

Key Features

• Military Standard (MS) Certified: Guarantees adherence to stringent material, dimensional, heat treatment, locking torque, and quality requirements.

• High-Strength (160 KSI Bolt Compatibility): Manufactured from heat-treated alloy steel specifically designed for use with bolts rated up to 160 KSI ultimate tensile strength.

• Deformed Thread Locking Mechanism: Provides reliable prevailing torque to resist loosening under vibration and dynamic loads, eliminating the need for secondary locking devices like cotter pins or lock wire in many applications.

• Heat-Treated Alloy Steel Construction: Offers exceptional tensile and proof load strength required for critical structural applications.

• Cadmium Plated for Corrosion Protection: Coated per QQ-P-416, providing a durable, sacrificial barrier against environmental corrosion.

• Standard Hexagon Drive: Allows for installation using standard sockets and wrenches.

Technical Specifications

• Part Number: MS17826-3

• Component Type: Self-Locking Nut, Hexagon

• Governing Specification: MS17826

• Material: Alloy Steel, Heat Treated (e.g., 4130, 4140, 8740 per standard). Rated for 160 KSI bolts.

• Finish: Cadmium Plated per QQ-P-416, Type II, Class 2.

• Thread Size: -3 (10-32 UNF-3B)

• Temperature Rating: Typically limited by the cadmium plating and locking feature performance, usually around 450°F (232°C). (Verify against the standard).

• Locking Feature: Deformed Thread Prevailing Torque.

Aircraft Compatibility

The MS17826-3 is a standard hardware component used in critical structural joints across all categories of aircraft, including military, commercial transport, and general aviation platforms from all major manufacturers (e.g., Textron, Boeing, Airbus, Lockheed Martin, Piper).

Crucial Note: The correct nut part number for a specific application (considering strength, temperature, and locking requirements) must be verified against the aircraft's Illustrated Parts Catalog (IPC), maintenance manual, or engineering drawings.

Applications

This nut is specifically designed for high-strength, vibration-prone bolted joints where a reliable self-locking feature is required. Common uses include:

• Airframe Structural Connections (wing attach points, spar joints, fuselage frames)

• Engine Mount Attachments

• Landing Gear Component Assembly

• Flight Control System Attachments

• Applications utilizing 160 KSI rated bolts (e.g., NAS6603 thru NAS6610 series).

Why Choose MS17826-3?

Choosing a genuine MS17826-3 nut is absolutely critical for structural integrity in high-stress applications. This nut is specifically heat-treated and designed to develop the full clamping force required when used with 160 KSI bolts, ensuring the joint meets its design strength. The locking feature is rigorously tested to meet specific prevailing torque values. Using a lower-strength nut (like an AN365 or MS21044) or a non-certified commercial part on a high-strength bolt will lead to thread stripping, insufficient clamp load, or failure of the locking mechanism under vibration, potentially resulting in catastrophic joint failure. The MS standard guarantees the material, heat treatment, and locking performance required for flight safety.

The MS17826-3 achieves its self-locking capability via prevailing torque, specifically through thread deformation. During manufacture, the upper threads of the nut are precisely deformed slightly out-of-round or axially displaced. As the mating bolt threads engage this deformed section, they must elastically displace the deformed nut threads to pass through. This interference creates a consistent frictional force between the mating thread flanks, resulting in a measurable torque required to rotate the nut even before any clamp load is applied. This prevailing torque is the locking mechanism; it resists the tendency of the nut to back off due to vibration or cyclic loading. The MS17826 standard specifies minimum and maximum prevailing torque values for the first installation and subsequent installations (typically up to 5 or 15 cycles, depending on the specification revision), ensuring consistent and reliable locking performance. The high-strength alloy steel is essential to withstand the stresses of thread deformation during manufacture and maintain the locking interference over the service life and temperature range.

Note: This is a flight-critical fastener intended for high-strength applications. It is often recommended practice to replace self-locking nuts each time they are removed, especially in critical structural locations or after exposure to elevated temperatures, as the locking effectiveness can degrade with reuse. Use of appropriate lubrication (as specified by the maintenance manual, considering cadmium plating) and tightening to the precise torque value defined in the maintenance documentation are essential for achieving the designed joint preload and ensuring fastener integrity.

Documentation

The definitive technical requirements for this component are detailed in Military Standard MS17826. These proprietary documents must be sourced directly from the relevant standards organizations (e.g., DoD ASSIST database) for complete engineering specifications.