AN4-13A - Aerospace Machine Bolt

AN4-13A – Aerospace Machine Bolt

Available now on the Airparts.aero Marketplace.

Overview

The AN4-13A is a military-standard, structural airframe bolt, a fundamental and ubiquitous component in aircraft construction and repair. Manufactured in strict accordance with Air Force/Navy (AN) standards, this bolt is engineered to provide reliable, high-strength fastening for a multitude of structural applications. Fabricated from high-tensile strength alloy steel and plated for corrosion resistance, the AN4-13A is designed to handle the shear and tension loads experienced during flight. The "A" suffix signifies an undrilled shank, indicating it is intended for use with a self-locking nut.

Key Features

• High-Tensile Strength: Fabricated from premium alloy steel (typically 4037 or 8740) and heat-treated to achieve a minimum tensile strength of 125,000 PSI, providing the robust performance required for primary structural joints.
• Precision Manufacturing: The bolt shank is centerless ground and the threads are rolled after heat treatment. This process creates a stronger, more fatigue-resistant fastener compared to bolts with machined or cut threads.
• Corrosion-Resistant Plating: Plated with a durable cadmium finish per specification QQ-P-416, Type II, Class 3. This plating provides excellent protection against environmental corrosion, ensuring the long-term integrity of the fastener.
• AN Standard Certified: As a certified AN-standard part, it guarantees full material traceability, dimensional accuracy, and quality control, ensuring it meets the stringent requirements for use in certified aircraft.

Technical Specifications

• Standard: AN4 (Airframe Bolt, Hex Head)
• Full Part Number: AN4-13A
• Material: High-Tensile Alloy Steel
• Finish: Cadmium Plated, Type II, Class 3
• Head Style: Hexagonal (Hex Head)
• Thread Specification: 1/4-28 UNF-3A
  • Nominal Diameter: 1/4 inch (0.250 inches)
  • Threads Per Inch: 28 (Fine Thread)
• Overall Length: 1-13/32 inches (1.406 inches), measured from under the head.
• Grip Length (Unthreaded Shank): 15/16 inch (0.938 inches)
• Drilled Shank: No (Indicated by "A" suffix)

Aircraft Compatibility

The AN4-13A is a universal structural fastener used across nearly every category of certified and experimental aircraft, including models from Textron Aviation, Piper, Cirrus, and many others. Its use is specified by the manufacturer's engineering drawings wherever a structural bolt with these precise dimensions is required.

• Common Applications:
  • Airframe Assembly: Joining ribs, stringers, and skins in wings, fuselage, and empennage sections.
  • Component Installation: Mounting flight controls, brackets, system hardware, and inspection panels.
  • Engine Baffles & Accessories: Securing engine baffles and various firewall-forward components that require a structural fastener.

Applications

The AN4-13A is the workhorse of airframe construction, ideal for creating strong, reliable bolted joints:

• Shear & Tension Joints: Designed to effectively carry both shear (side-to-side) and tension (pulling) loads. The grip length must be properly matched to the material thickness to ensure shear loads are borne by the unthreaded shank.
• Use with Self-Locking Nuts: The undrilled "A" designation makes it the standard choice for use with self-locking nuts, such as an AN365 or MS21044 series, providing a secure, vibration-resistant connection.

Why Choose AN4-13A?

The structural integrity of an aircraft depends on the quality of every fastener. Using a genuine AN4-13A bolt guarantees you are installing a component with a certified material strength, a protective plating designed for aviation environments, and precise dimensional tolerances. Substituting with uncertified commercial-grade hardware is extremely dangerous, as it can lead to joint failure from vibration, corrosion, or overloading. For any airworthy repair, trust only certified AN-standard hardware.

Order Your AN4-13A Bolts Now

Build and maintain your aircraft with the certified, high-strength hardware the industry trusts. Visit Airparts.aero to order your AN4-13A structural airframe bolts today.

The AN bolt part numbering system provides a complete and precise description of the fastener. In AN4-13A:

• AN: Signifies "Air Force/Navy," the original standardizing body.
• 4: Indicates the nominal shank diameter in sixteenths of an inch (4/16" or 1/4").
• 13: The first digit "1" represents a full inch in length, and the second digit "3" represents an additional 3/8 of an inch. Thus, the total length is 1-3/8" (1.375"). Note: The nominal length is often rounded, the actual length is 1-13/32" or 1.406".
• A: Denotes an undrilled shank, for use with a self-locking nut. If the "A" were absent (AN4-13), the shank would be drilled for a cotter pin to be used with a castellated nut.

This standardized system ensures that mechanics and engineers can select the exact hardware required for a specific structural joint with confidence and precision.

Note: This is a flight-critical structural component. Always verify the correct bolt part number (diameter and length) from the applicable aircraft maintenance manual or Illustrated Parts Catalog (IPC). The grip length must be appropriate for the material thickness being fastened. Installation requires the use of a calibrated torque wrench and a corresponding certified nut.

AN Series Bolts Reference:   [ Click Here ]

Product Description: Length: 1-13/32, Grip: 15/16", Thread: 1/4-28
Cadmium plated steel, undrilled shank



AN4-13A  Datasheet Features and Specification

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