AN4-14A – 1/4-28 x 1-1/2" Hex Head Bolt, Alloy Steel, Cadmium Plated
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Overview
The AN4-14A is a high-strength, general-purpose aerospace fastener manufactured to the foundational Air Force-Navy (AN) standard. This hex head bolt is engineered from heat-treated alloy steel for use in critical structural applications requiring high tensile and shear strength. With a 1/4-inch diameter, a 1-1/2-inch nominal length, and a substantial 1-1/16-inch grip, this bolt is designed for robust clamping and load-bearing joints. The "A" suffix in the part number signifies an undrilled shank, indicating its intended use with self-locking nuts or other approved locking devices.
Protected by a durable cadmium plating for superior corrosion resistance, the AN4-14A is a ubiquitous and essential component in aircraft construction and maintenance. Its adherence to the AN specification ensures complete traceability, uniform quality, and the mechanical performance required for flight-critical installations.
Key Features
High-Tensile Alloy Steel: Fabricated from premium alloy steel (typically 4140 or 8740) and heat-treated to a minimum tensile strength of 125,000 PSI for maximum load-carrying capability.
Cadmium Plating: Coated with a sacrificial cadmium layer per QQ-P-416, providing excellent protection against environmental corrosion and ensuring consistent torque-tension relationships.
Rolled Threads: Features 1/4-28 UNF-3A threads that are cold-rolled, a process that improves the material's grain structure and dramatically increases resistance to fatigue failure compared to machine-cut threads.
Undrilled Shank ("A" Type): The solid, un-drilled shank is designed for use with a variety of self-locking nuts, providing secure fastening in a wide range of tension and shear applications.
Substantial Grip Length: A 1-1/16-inch grip (unthreaded shank) ensures that shear loads are borne by the full diameter of the bolt for maximum joint strength.
AN Standard Compliance: Guarantees every aspect of the bolt—from material chemistry to dimensional tolerances—meets the rigorous standards required for airworthy components.
Technical Specifications
Part Number: AN4-14A
Component Type: Hex Head Machine Bolt
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): 1-1/2 inches (1.500 inches)
Grip Length (Unthreaded Shank): 1-1/16 inches (1.063 inches)
Thread Specification: 1/4-28 UNF-3A
Aircraft Compatibility
The AN4-14A is a standard hardware item used across the entire spectrum of aviation, from light piston aircraft to the largest transport category jets. It is specified in countless locations on aircraft manufactured by:
Textron Aviation (Cessna, Beechcraft, Hawker)
Boeing
Airbus
Bombardier
Embraer
Piper, Cirrus, Diamond, and all other major OEMs.
Note: Verification of applicability is the responsibility of the installer. The grip length must be correctly matched to the total thickness of the material being joined. Always consult the current version of the aircraft's Illustrated Parts Catalog (IPC) or maintenance manual to confirm part number eligibility.
Applications
Airframe structural connections (e.g., attaching brackets to spars or ribs).
Engine accessory and component mounting.
Landing gear system assembly and attachments.
Flight control surface and system component installation.
Any joint requiring a high-strength, 1/4-inch diameter bolt with a 1-1/16-inch grip length.
Why Choose AN4-14A?
The use of certified aerospace hardware is non-negotiable for flight safety. An AN4-14A bolt guarantees the precise material properties, heat treatment, and manufacturing processes (like rolled threads) that are essential for resisting the unique stresses of flight, including vibration and cyclic loading. The substitution of a commercial-grade bolt, which lacks these controlled attributes, would introduce a direct and catastrophic risk of joint failure. This certified fastener is the only choice for an airworthy repair.
The engineering principle dictating the use of a specific AN bolt often centers on the critical dimension of its grip length. For a shear joint to achieve its maximum design strength, the shear plane must pass through the unthreaded shank (grip) of the bolt. The AN fastener system provides a comprehensive range of grip lengths for each diameter to ensure this requirement can be met. The 1.063-inch grip of the AN4-14A is designed to pass completely through the material stack-up, allowing the shear loads to be distributed across the bolt's full, nominal diameter. If the threads were to bear these shear loads, the smaller root diameter and inherent stress concentrations of the thread profile would significantly reduce the joint's ultimate strength and fatigue life, creating a point of failure. Proper bolt selection is therefore a critical maintenance task.
Note: This is a flight-critical hardware component. Installation must be performed by a certified mechanic. A calibrated torque wrench must be used to apply the correct torque value specified in the maintenance manual to achieve proper clamp load (preload). This bolt must be paired with a corresponding certified aerospace-grade self-locking nut (e.g., MS21044N4 or MS21045N4) to ensure the joint remains secure.
Documentation
The specifications for this fastener are maintained under the National Aerospace Standards (NASM), which have superseded many of the original AN drawings. Publicly accessible summaries of these standards can often be found through standards organizations and authorized hardware suppliers.