MS24665-300 – Aerospace Cotter Pin (3/32 x 3/4)
Available now for order on the Aerospace Hardware Marketplace.
Overview Section
The MS24665-300 is a high-integrity Split Cotter Pin governed by the Military Standard (MS) system. It is a critical secondary locking device used throughout aircraft structures and engine assemblies to prevent nuts, pins, and other fasteners from rotating or backing off due to high-frequency vibration.
The designation follows the MS24665 standard for "Pin, Cotter (Split)." The dash number -300 defines its precise dimensions: a nominal diameter of 3/32 inch and a nominal length of 3/4 inch. These pins are typically manufactured from Corrosion-Resistant Steel (CRES) or Carbon Steel with a protective coating to ensure longevity in harsh aviation environments.
Key Features Section
Vibration Security: Acts as a positive locking mechanism when inserted through a hole in a bolt or shaft and the castellations of a nut (castle nut).
Corrosion-Resistant Material: Typically fabricated from Stainless Steel (300 series) or Cadmium-Plated Carbon Steel, preventing material degradation and seizing.
Malleable Design: The tines are engineered to be bent easily by hand or tool without cracking, ensuring a secure "wrap" around the fastener.
Standardized Sizing: Manufactured to strict aerospace tolerances for diameter and length to ensure a proper fit in pre-drilled hardware.
High Temperature Stability: Unlike nylon-insert locking nuts, these pins maintain their locking integrity in high-heat zones like engine bays and wheel-well assemblies.
Technical Specifications Section
Part Number: MS24665-300
Diameter (Nominal): 3/32 inch (0.094")
Length (Nominal): 3/4 inch (0.750")
Material: Corrosion-Resistant Steel (CRES) per AMS 5688 or Carbon Steel per ASTM A510.
Finish: Passivated (for Stainless) or Cadmium Plated per QQ-P-416 (for Carbon Steel).
End Style: Standard extended prong (square cut or chisel point).
Governing Specification: MS24665 / NASM24665.
Aircraft Compatibility Section
General Aviation and Commercial Airframes: Used in nearly every safety-wire or cotter-pin application on flight control linkages, engine mounts, and access panels.
Landing Gear Assemblies: Critical for securing axle nuts and torque link pins where high-load vibration is constant.
Flight Controls: Used to secure clevis pins and rod ends in primary and secondary control paths.
Note: The MS24665-300 is a flight-critical hardware item. The aircraft Illustrated Parts Catalog (IPC) or Maintenance Manual is the final authority for determining the required pin size and material for any specific application.
Applications Section
Securing Castle Nuts (AN310 / AN320): Preventing rotation of nuts on structural bolts.
Clevis Pin Retention: Ensuring clevis pins remain in place within control cables and pulleys.
Drain Plug Security: Locking fuel or oil drain plugs to prevent accidental opening during flight.
Why Choose the MS24665-300?
The MS24665-300 is an essential "single-use" safety component. In aerospace, a fastener backing off can lead to the loss of a control surface or engine failure. Using a commercial hardware-store cotter pin instead of a certified MS24665-300 risks: 1) Brittle Failure: Non-certified pins may snap when bent or under vibration; 2) Corrosion: Improper plating leads to rapid oxidation and weakening of the pin; and 3) Improper Fit: Commercial tolerances may allow the pin to "jiggle" in the hole, leading to fretting and eventual failure. The MS certification ensures the material ductility and shear strength required for flight safety.
The mechanical safety of the MS24665-300 relies on its ductility and shear resistance. When the tines are bent over the nut or bolt, they must not show signs of "crazing" or surface cracking, as these would be points of failure under the high-frequency vibration of a running engine. FAA and military guidelines strictly prohibit the reuse of cotter pins; once bent and straightened, the metal undergoes work-hardening, significantly reducing its ability to resist fatigue. The MS24665 standard ensures the pin can survive a full 90-degree to 180-degree bend while maintaining the shear strength necessary to block a nut from rotating.
Note: The MS24665-300 is a mandatory replacement item. Always install a new pin during any maintenance where a fastener is disturbed. Ensure the pin is installed so that the head (eye) is pulled tight against the hole and the tines are bent securely against the nut or bolt flats.
Documentation
MS24665 Military Standard Drawing: Contains the full dimensional and material table.
AC 43.13-1B: FAA Acceptable Methods, Techniques, and Practices for proper cotter pin installation.