MS17825-4 - Textron Aviation OEM Slotted Castellated Self-Locking Nut

MS17825-4 – Textron Aviation OEM 1/4-28 Castellated Self-Locking Nut

Available now on the Airparts.aero Marketplace.

Overview

The MS17825-4 is a specialized, high-security fastener, supplied as a genuine Textron Aviation Original Equipment Manufacturer (OEM) component, designed for the most flight-critical bolted joints. This nut represents the pinnacle of fastener security by incorporating a dual-locking system. It combines the prevailing torque feature of a nylon self-locking insert with the positive locking capability of a castellated nut designed for use with a cotter pin. This redundant design provides two independent mechanisms to prevent loosening from vibration and ensure the integrity of the connection.

Manufactured from cadmium-plated steel and rated for service up to 250°F, this 1/4-28 UNF nut is specified in applications where the consequence of fastener failure is catastrophic. As a Textron Aviation OEM part, it is the factory-certified component for use on critical assemblies throughout the Cessna, Beechcraft, and Hawker fleets, guaranteeing adherence to the highest standards of safety and airworthiness.

Key Features

• Dual Redundant Locking System: Incorporates both a prevailing torque nylon insert and castellated slots for a cotter pin, providing the ultimate level of fastener security.

• Prevailing Torque Nylon Insert: A captive nylon collar grips the bolt threads to provide constant frictional resistance, preventing loosening from vibration and maintaining joint preload.

• Castellated for Positive Locking: The slotted design allows for the installation of a cotter pin through the nut and a drilled-shank bolt, creating a physical barrier that prevents the nut from backing off.

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

• 250°F Temperature Rating: Suitable for a wide range of airframe applications, limited by the nylon locking element.

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

Technical Specifications

• Part Number: MS17825-4

• Component Type: Hexagon Castellated Self-Locking Nut

• OEM Authority: Textron Aviation

• Governing Specification: MS17825

• Material: Steel, Cadmium Plated

• Locking Element: Nylon Insert

• Thread Specification: 1/4-28 UNF-3B

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

• Locking Principles:

  1. Prevailing Torque

  2. Positive Lock (with cotter pin)

Aircraft Compatibility

As a Textron Aviation OEM part, this nut is specified for the most critical applications on their aircraft. The underlying MS standard makes it a common choice for similar applications across the aerospace industry.

• Primary Textron Aviation Platforms:

  • Cessna Citation Series

  • Beechcraft King Air Series

  • Hawker Business Jets

• General Aerospace Usage: Any application where redundant fastener locking 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.

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

• Landing Gear Systems: Securing major structural components of the landing gear assembly.

• Rotor Systems: Used in critical attachments in helicopter rotor heads and flight controls.

Why Choose MS17825-4?

For the applications where this nut is specified, there is no substitute. It embodies a "belt-and-suspenders" engineering philosophy for flight-critical connections. The dual-locking mechanism provides a level of security that a standard locknut or a standard castle nut alone cannot. Choosing the Textron Aviation OEM part ensures you are installing a fully certified component that meets both the prevailing torque and positive lock requirements of the aircraft's original, type-certified design, where the margin for error is zero.

The MS17825-4 fastener is an embodiment of the design principle of dissimilar redundancy, a cornerstone of creating fault-tolerant aerospace systems. The two locking mechanisms are not only redundant but also operate on different physical principles. The nylon insert provides a prevailing torque lock, which is a friction-based system excellent at damping high-frequency vibration and maintaining bolt preload. The castellated nut and cotter pin provide a positive, or mechanical, lock. This system is not dependent on friction or preload. Its function is to provide a physical barrier that prevents disassembly. In a failure analysis scenario, this means the two systems are unlikely to fail from the same cause; the nylon insert maintains the joint's rigidity, while the cotter pin ensures the physical connection, providing two layers of defense against 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 available slot—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