AN4-12 - Textron Aviation OEM Steel Hex Head Bolt

AN4-12 – Textron Aviation OEM Drilled Shank Hex Bolt

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Overview

The AN4-12 is a high-strength, hex head bolt that holds dual authority as a component built to the exacting Air Force-Navy (AN) standard and as a genuine Textron Aviation Original Equipment Manufacturer (OEM) part. This fastener is engineered for the most critical joints, particularly those in shear, where an absolutely secure, positive locking mechanism is required. Its defining feature is the drilled shank, which is designed to be used in conjunction with a castellated nut and cotter pin to physically prevent rotation and ensure the fastener cannot loosen under any operating conditions.

Constructed from heat-treated alloy steel and protected by cadmium plating, this 1/4-inch diameter by 1-1/4-inch length bolt is a cornerstone of flight-critical assemblies. As a Textron Aviation OEM part, it is the factory-specified hardware for countless applications on Cessna, Beechcraft, and Hawker aircraft, guaranteeing the ultimate level of safety, traceability, and airworthiness.

Key Features

• Textron Aviation OEM Certified: Supplied with the full traceability and quality assurance of Textron Aviation, guaranteeing it is the correct, factory-approved part for their fleet.

• Drilled Shank for Positive Locking: The hole in the threaded portion is designed for a cotter pin and castellated nut (e.g., AN310), creating a lock that is physical, verifiable, and not dependent on preload.

• High-Tensile Alloy Steel: Forged from premium alloy steel and heat-treated to a minimum tensile strength of 125,000 PSI for maximum joint strength.

• Optimized for Shear Applications: The combination of a substantial grip length and a positive locking system makes this bolt the standard choice for linkages, clevises, and shear pins.

• Rolled Threads: Features 1/4-28 UNF-3A threads that are cold-rolled, a superior manufacturing process that increases fatigue resistance exponentially compared to cut threads.

• AN Standard Compliance: Fully conforms to the AN4 specification, ensuring the highest level of quality control for materials and dimensions.

Technical Specifications

• Part Number: AN4-12

• Component Type: Drilled Shank Hex Head Bolt

• OEM Authority: Textron Aviation

• Governing Specification: AN4 / NASM4

• Material: Alloy Steel (e.g., 4140, 8740), heat-treated

• Minimum Tensile Strength: 125,000 PSI

• Finish: Cadmium Plate per QQ-P-416, Type II, Class 2

• Diameter: 1/4 inch (0.250 inches)

• Nominal Length (under head to end): 1-1/4 inches (1.250 inches)

• Grip Length (Unthreaded Shank): 13/16 inch (0.813 inches)

• Thread Specification: 1/4-28 UNF-3A

Aircraft Compatibility

As a Textron Aviation OEM part, this fastener is specified in numerous flight-critical locations across their product lines. As an AN-standard bolt, its use is universal throughout the aerospace industry.

• Primary Textron Aviation Platforms:

  • Cessna Citation Series Business Jets

  • Beechcraft King Air, Baron, and Bonanza

  • Cessna Caravan and Piston Aircraft (172, 182, 206)

  • Hawker Business Jets

• General Aerospace Usage: A fundamental component in the assembly of nearly all certified aircraft.

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.

Applications

• Primary Flight Control Systems: Used to attach control surfaces, bellcranks, push-pull rods, and control cable linkages.

• Landing Gear Systems: Essential for connecting torque links (scissors), struts, and retraction mechanisms.

• Engine Controls: Used in throttle, propeller, and mixture control linkages where failure is not an option.

Why Choose this AN4-12?

This component provides the dual assurance of meeting the public AN aerospace standard and the specific endorsement of Textron Aviation. In flight-critical applications, particularly in control systems, the positive lock of a cotter pin is the mandated method of securing a fastener. Choosing this OEM part ensures you are installing a fully traceable, airworthy component with the correct material properties, exactly as specified in the aircraft's original, type-certified design.

The engineering mandate for a drilled shank bolt like the AN4-12 in primary flight control systems is its provision of a "positive lock." This method is fundamentally different from and superior to a "prevailing torque" lock for such applications. A prevailing torque nut relies on friction, which can be overcome or degrade. A positive lock, created by a cotter pin passing through both the castellated nut and the bolt, is a physical barrier. This system is designed to maintain the integrity of the joint even in the highly improbable event of a complete loss of torque or preload. It physically prevents the nut from backing off, ensuring the connection remains intact. This fail-safe principle is the bedrock of safety in designing and maintaining systems where a single fastener failure would be catastrophic.

Note: This is a flight-critical hardware component. Installation must be performed by a certified mechanic. The castellated nut should be torqued to the specific value in the maintenance manual, which is often a low value intended only to remove play from the joint. If the nut slot and bolt hole do not align, the nut must be tightened to the next alignment point; never loosened. A new cotter pin must be used for every installation and bent properly to secure it.

Documentation

The base standard for this part is maintained under the National Aerospace Standards (NASM). OEM-specific application and installation data is contained within the Textron Aviation maintenance and structural repair manuals.