1505-8 – Stainless Steel MS24665-13 Replacement Cotter Pin (1/16" x 1/2") for Genesis / S-Tec Systems
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The 1505-8 (frequently cross-referenced to the military standard MS24665-13) is a high-grade stainless steel split cotter pin designed for securing threaded fasteners in safety-critical aerospace and automotive applications. Measuring 1/16 inch in diameter with a 1/2 inch nominal length, this pin is a fundamental component of "positive locking" systems. It is used to prevent nuts, pins, or shafts from rotating or vibrating loose, which is a primary requirement for airworthiness in flight control and engine assemblies.
Manufactured from 300-series Corrosion Resistant Steel (CRES), the 1505-8 is specifically chosen for areas exposed to high moisture, exhaust gases, or de-icing fluids where carbon steel pins would succumb to rapid oxidation. Its "chisel point" or "extended prong" design allows for easy insertion into drilled bolts and castellated nuts, providing a reliable mechanical interference that remains effective even under the extreme high-frequency vibrations characteristic of turbine and piston engine environments.
Key Features
302/304 Stainless Steel Construction: Provides exceptional resistance to rust and environmental degradation, ensuring the pin does not become brittle or "seize" within the fastener hole over long service intervals.
Extended Prong Design: Features one leg slightly longer than the other, allowing the technician to easily separate and "roll" the prongs over the nut or bolt head using standard pliers.
Precision 1/16" Diameter: Calibrated for a high-tolerance fit in standard AN3 and AN4 series drilled bolts and clevis pins, minimizing "slop" or mechanical wear within the hole.
Annealed for Ductility: The stainless steel is heat-treated to a specific softness, allowing the prongs to be bent 90° to 180° multiple times during installation without snapping or work-hardening.
Standard Chisel Point: The tapered ends facilitate rapid "blind" installation in confined spaces, such as inside wheel wells or engine nacelles.
Technical Specifications
Part Number: 1505-8 (Commercial / OEM Cross-Ref)
MS Standard: MS24665-13 (Equivalent)
Diameter: 1/16 inch (0.0625")
Length: 1/2 inch (0.500") — Measured from under the eye to the end of the shortest prong.
Material: 302/304 Stainless Steel (CRES) per AMS 5688
Finish: Passivated per AMS 2700
Head Style: Hammerhead / Eyelet
Prong Style: Extended Prong / Chisel Point
Aircraft Compatibility
Cessna, Piper, & Beechcraft: Standard for securing castellated nuts on flight control linkages, throttle cables, and door hinges.
Boeing & Airbus: Used in non-structural secondary systems and cabin interior monument securement.
Experimental Aircraft: A staple for RV-series builders for brake line clevis pins and rudder pedal assemblies.
Note: Always refer to the Illustrated Parts Catalog (IPC) for the specific diameter and length required; a cotter pin that is too thin for the hole can shear under vibration.
Applications
The 1505-8 is utilized for Positive Fastener Locking. Its primary roles include:
Castellated Nut Retention: Preventing the nut from backing off a drilled bolt on landing gear or engine mounts.
Clevis Pin Securing: Locking the pivot pins in control yokes and brake master cylinder linkages.
Castle Nut Safety: Used on castellated axle nuts for small aircraft nose wheels.
Why Choose 1505-8?
Choosing a genuine 300-series stainless pin like the 1505-8 is critical for preventing galvanic corrosion. When used with aluminum or stainless steel hardware, a standard zinc-plated steel pin can create a battery effect, leading to "frozen" fasteners or structural pitting. The 1505-8 maintains its structural integrity across a massive temperature range, ensuring that your secondary locking mechanism doesn't fail due to heat-soak near exhaust manifolds or cryogenic cooling at high altitudes.
The mechanical security provided by the 1505-8 relies on the principle of Secondary Redundancy. In a "safety-critical" joint, the cotter pin acts as a physical obstruction that prevents the nut from rotating relative to the bolt, even if the primary torque (preload) is lost. The physics of the installation require that the pin occupies at least 75% of the hole diameter to prevent "shear fatigue." Proper installation—either via the "Preferred" method (wrapping prongs over the end of the bolt) or the "Optional" method (wrapping prongs around the sides of the nut)—ensures that the pin remains in a state of passive tension, preventing it from vibrating against the walls of the hole and causing "elongation" over time.
Note: This is a "one-time use" safety component. Never straighten and reuse a cotter pin, as the metal becomes work-hardened and prone to snapping during the second installation. Ensure the prongs are bent tightly against the fastener to prevent snagging on clothing or skin during maintenance. Installation must be performed in accordance with FAA AC 43.13-1B, Chapter 7.