MS24665-353 - Military Standard Aerospace Cotter Pin

MS24665-353 – Military Standard Aerospace Cotter Pin AN380-4-4

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Overview

The MS24665-353 is a military-standard cotter pin, a flight-critical piece of safety hardware used throughout all types of aircraft. This component is engineered to provide a simple, reliable, and visually verifiable method of securing castellated nuts, bolts, and other fasteners against loosening due to vibration. Manufactured in strict accordance with the MS24665 specification, this cotter pin is fabricated from high-quality carbon steel and plated for corrosion resistance, ensuring its integrity in the demanding aerospace environment. To better describe, this item is a half round, cylindrical, or flat piece of metal, bent to form a straight or crimped two-pronged device with an eye at one end, for inserting in a hole drilled at right angle to the axis of the stud, shaft, or like item. Its ends are separable or one end is bent to hold it in place.

Key Features

• Positive Locking Device: Its sole purpose is to provide a positive mechanical lock for castellated nuts, preventing them from rotating and backing off a bolt or stud. This is a primary method of securing critical structural hardware.
• High-Quality Carbon Steel: Fabricated from a specified carbon steel alloy that provides the optimal balance of ductility (for easy bending of the tines) and shear strength (to resist failure).
• Corrosion-Resistant Plating: Plated with a durable cadmium finish per specification QQ-P-416, Type II, Class 3. This plating provides excellent protection against corrosion, ensuring the pin does not degrade in service.
• Extended Prong Design: Features one tine (prong) that is slightly longer than the other. This standard design feature aids in the separation and bending of the tines during installation.
• MS Certified Standard: As a certified Military Standard part, it guarantees the material, dimensions, and quality control required for use in certified aircraft, ensuring full airworthiness. It is the superseding part number for the legacy AN380-4-4 cotter pin.

Technical Specifications

• Standard: MS24665 (Pin, Cotter, Split)
• Alternate Part Number: AN380-4-4
  
• Full Part Number: MS24665-353
• Legacy Part Number: AN380-4-4
• Material: Carbon Steel
• Finish: Cadmium Plated, Type II, Class 3
• Nominal Diameter: 1/8 inch (0.125 inches)
• Length: 1 inch (1.000 inches), measured from under the head loop.
• Point Type: Extended Prong, Square Cut

Aircraft Compatibility

The MS24665-353 is a universal piece of hardware used on virtually every type of aircraft ever built, including all models from Textron Aviation, Piper, Cirrus, and others. Its use is specified any time a 1/8" x 1" cotter pin is required to secure a castellated nut, typically on larger diameter bolts (e.g., AN9, AN10, AN11).

• Common Applications:
  • Securing nuts on flight control bolts.
  • Locking axle nuts on main and nose landing gear.
  • Securing bolts on engine mounts and other critical structural components.
  • Used in countless other mechanical assemblies throughout the airframe and engine.

Applications

The MS24665-353 is a critical safety-of-flight component:

• Securing Castellated Nuts: Installed through the drilled hole in a bolt or stud, with the tines spread over a castellated (slotted) nut like the AN310 or AN320.
• Preventing Loosening: Acts as a physical barrier that prevents the nut from rotating loose under any operational condition, most notably high vibration.
• Visual Verification: Provides an easy, visual confirmation during pre-flight and maintenance inspections that the fastener is properly secured.

Why Choose MS24665-353?

The failure of a cotter pin can lead to the loosening and separation of a critical bolted joint, which can be catastrophic. Using a genuine MS24665-353 cotter pin ensures you are installing a part with a known material strength and certified quality. Substituting with a non-certified, commercial-grade cotter pin from a hardware store is extremely dangerous, as these parts lack the material traceability, specific strength properties, and corrosion resistance required for aviation use. For any safety-of-flight application, trust only certified Mil-Spec hardware.

Order Your MS24665-353 Cotter Pins Now

Stock your shop with the flight-critical, certified hardware essential for safe and airworthy maintenance. Visit Airparts.aero to order your MS24665-353 cotter pins today.

The MS24665-353 cotter pin is a simple yet elegant solution for securing critical fasteners, operating purely on the principle of mechanical interference. After a castellated nut is torqued to its specified value, it is slightly rotated (tightened only) to align one of its slots with the hole in the bolt shank. The cotter pin is then inserted, and the tines are bent. Per standard aviation practice (as detailed in AC 43.13-1B), one tine is bent up and over the end of the bolt, while the other is bent down against the side of the nut. This creates a secure lock that physically prevents the nut from rotating in either direction. The material's ductility is key, as it must bend without fracturing but remain strong enough to resist shearing off under torsional load if the nut attempts to loosen.

Additional Specifications

Note: Cotter pins are strictly single-use items. A pin that has been installed and bent must never be straightened and reused, as the bending process work-hardens the metal and creates stress risers that can lead to fracture. Always use a new pin for every installation.

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