AN3H-13A – 10-32 x 1-3/8" Drilled Head Hex Bolt, Alloy Steel, Cadmium Plated
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Overview
The AN3H-13A is a high-strength, drilled-head hex bolt manufactured to the rigorous Air Force-Navy (AN) standard, representing a fundamental component of safe and reliable aircraft assembly. This fastener is specifically engineered for tension-loaded joints in high-vibration environments where a positive locking mechanism is mandatory. Its defining feature is the set of holes drilled through the flats of the hexagonal head, which are designed for the installation of safety wire (lockwire).
This bolt, often referred to by the base number AN3-13A, has a 3/16-inch diameter and a 1-3/8-inch nominal length. It is forged from heat-treated alloy steel and protected by a durable cadmium plating for exceptional strength and corrosion resistance. Its adherence to the AN specification ensures the full traceability and quality control required for any flight-certified application.
Key Features
Drilled Head for Lockwiring: The hexagonal head is cross-drilled to facilitate the installation of safety wire, creating a positive, anti-rotation locking mechanism that is visually verifiable.
High-Tensile Alloy Steel: Manufactured from heat-treated alloy steel (typically 4140 or 8740) to a minimum tensile strength of 125,000 PSI, providing exceptional strength for tension applications.
Cadmium Plating: Coated with a sacrificial cadmium layer per QQ-P-416 for superior corrosion resistance and consistent lubricity, ensuring accurate torque application.
Rolled Threads: Features #10-32 UNF-3A threads that are cold-rolled, not cut. This process significantly increases fatigue life by improving the grain structure at the critical thread roots.
Undrilled Shank: The "A" designation signifies a solid, un-drilled shank, for use with various types of nuts where the primary locking feature is the safety-wired head.
AN Standard Compliance: As a true AN-standard part, it guarantees interchangeability, dimensional accuracy, and material integrity for airworthy installations.
Technical Specifications
Part Number: AN3H-13A (commonly referred to as AN3-13A, Drilled Head)
Component Type: Drilled Head Hexagonal Bolt
Governing Specification: AN3H / NASM3H
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: 3/16 inch (0.1875 inches)
Nominal Length (under head to end): 1-3/8 inches (1.375 inches)
Grip Length (Unthreaded Shank): 1 inch (1.000 inches)
Thread Specification: #10-32 UNF-3A
Aircraft Compatibility
The AN3H-13A is a standard hardware component, not specific to a single aircraft model. It is used ubiquitously across all segments of aviation where engineering drawings specify a 10-32 drilled head hex bolt of this length. Applications span:
Military Aircraft
Commercial and Transport Category Aircraft
General Aviation (Piston and Turbine)
Rotorcraft
Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the applicable Illustrated Parts Catalog (IPC) or maintenance manual to confirm part number eligibility for a specific location.
Applications
Powerplant: Securing engine accessories, magnetos, vacuum pumps, engine baffles, and exhaust system brackets.
Airframe: Attaching structural brackets, inspection panels, and system components located in areas of high vibration.
Systems: Mounting hydraulic components, filter housings, and fluid line clamps.
Why Choose AN3H-13A?
In aviation, there is no substitute for certified hardware. An AN3H-13A bolt guarantees the specific material chemistry, heat treatment, and manufacturing processes essential for flight safety. The use of a commercial-grade or non-traceable bolt would introduce a catastrophic risk of failure due to lower tensile strength, poor fatigue life, and susceptibility to corrosion. This certified fastener, with its provision for positive locking, ensures the joint will remain secure under the most demanding operational conditions.
The application of an AN3H-13A bolt is inseparable from the technique of safety wiring, a fundamental skill governed by standard practices like FAA AC 43.13-1B. The engineering principle is to create a positive lock that uses tensile force to prevent fastener rotation. In the most common "double-twist" method, a single strand of wire (e.g., MS20995C20) is passed through one hole in the bolt head, routed to a second fastener or anchor point, and then back. The two strands are then twisted together using specialized pliers. The technique is precise: the wire must be routed such that any tendency for the fastener to loosen (turn counter-clockwise) places the wire into tension. Furthermore, the twists themselves—typically 6 to 8 per inch for .032" wire—create a rigid, unitized member that resists unwinding. The final "pigtail" is cut and bent back to create a neat, safe installation. This simple, visually inspectable method remains one of the most reliable and trusted locking mechanisms in all of aerospace engineering.
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 preload. Safety wire must be installed in accordance with standard practices, ensuring it is new, clean, properly tensioned, and twisted correctly, with the pigtail bent back to prevent injury.
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.