MS17825-6 - Textron Aviation OEM Slotted Castellated Self-Locking Nut

MS17825-6 – Textron Aviation OEM 3/8-24 Castellated Self-Locking Nut

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Overview

The MS17825-6 is a maximum-security fastener, supplied as a genuine Textron Aviation Original Equipment Manufacturer (OEM) component, and designed for the most flight-critical 3/8-inch bolted joints. This nut is engineered with a dual-locking system, providing two distinct and independent mechanisms to ensure fastener integrity. It combines the consistent, vibration-damping prevailing torque of a nylon self-locking insert with the infallible, positive lock of a castellated nut designed for a cotter pin.

This redundant design philosophy makes the MS17825-6 the mandated hardware for primary structural and flight control attachments where the consequence of failure is unthinkable. Manufactured from high-strength, cadmium-plated steel and rated for service up to 250°F, this component represents the highest standard of fastener security. As a Textron Aviation OEM part, it is the certified and fully traceable choice for maintaining the airworthiness of Cessna, Beechcraft, and Hawker aircraft.

Key Features

• Dual Redundant Locking System: Integrates a prevailing torque nylon insert and castellated slots for a cotter pin, providing two independent layers of security against loosening.

• Prevailing Torque Nylon Insert: A captive nylon collar provides a constant frictional grip on the 3/8-24 bolt threads, maintaining crucial preload and resisting high-frequency vibration.

• Castellated for Positive Locking: The slotted design allows for the installation of a cotter pin through the nut and a drilled-shank bolt (e.g., AN6 series), creating an absolute mechanical barrier to rotation.

• High-Strength Steel Construction: Fabricated from aerospace-grade steel and plated with cadmium per QQ-P-416 for high strength and exceptional corrosion resistance.

• 250°F Temperature Rating: Suitable for a wide range of demanding airframe applications within its specified thermal limits.

• Textron Aviation OEM Certified: Guarantees the part is the fully traceable, factory-specified component for Textron Aviation aircraft.

Technical Specifications

• Part Number: MS17825-6

• Component Type: Hexagon Castellated Self-Locking Nut

• OEM Authority: Textron Aviation

• Governing Specification: MS17825

• Material: Steel, Cadmium Plated

• Locking Element: Nylon Insert

• Thread Specification: 3/8-24 UNF-3B

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

• Locking Principles:

  1. Prevailing Torque (Friction Lock)

  2. Positive Lock (Mechanical Lock via Cotter Pin)

Aircraft Compatibility

As a Textron Aviation OEM part, this nut is specified for the most critical structural and control system applications across their product lines, especially on larger, higher-performance aircraft.

• Primary Textron Aviation Platforms:

  • Cessna Citation Series (Latitude, Longitude, etc.)

  • Beechcraft King Air Series

  • Hawker Business Jets

• General Aerospace Usage: Any application on any airframe where redundant locking for a 3/8-inch fastener is mandated by the design authority.

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 for a specific joint.

Applications

• Primary Flight Control Systems: Attaching control surfaces like ailerons, elevators, and rudders to their hinges and actuators.

• Major Structural Joints: Used in wing-to-fuselage attachments, landing gear trunnions, and other primary structural connections.

• Engine and Pylon Mounts: Used in critical engine and powerplant attachment points.

Why Choose MS17825-6?

For the major structural applications where this 3/8-inch nut is specified, nothing else is acceptable. It represents the highest level of fastener security through designed redundancy. The dual-locking mechanism provides a level of safety that a standard locknut or a standard castle nut alone cannot. Using the Textron Aviation OEM part guarantees you are installing a fully certified component that meets the dual specifications required by their engineering drawings for these high-consequence joints, where the margin for error is zero.

The MS17825-6 fastener is a prime example of applying the engineering principle of dissimilar redundancy to a single component. The two locking mechanisms are designed to protect against different failure modes. The nylon insert provides a prevailing torque (friction) lock, which is highly effective at damping high-frequency vibrations and maintaining the bolt's axial preload. The castellated nut and cotter pin provide a positive (mechanical shear) lock. This secondary system is not dependent on friction or preload and is designed to provide a physical barrier to prevent disassembly. This ensures that even in a highly improbable scenario where the primary friction lock is compromised or the joint loses its clamp load, the mechanical lock of the cotter pin will ensure the physical connection remains intact, preventing catastrophic failure.

Note: This is a flight-critical hardware component. Installation must be performed by a certified mechanic in strict accordance with the maintenance manual. The nut should be torqued to the specified value. If the slots in the nut do not align with the hole in the bolt, the nut must be tightened to the next alignment point—never loosened. The 250°F temperature limit must be strictly observed. A new cotter pin must be used for every installation.

Documentation

The military standard governing 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 manuals.

• ASSIST Document Summary Page for MS17825: http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=36599