How to Choose the Right AN Fittings for Your DIY Auto Repair

How to Choose the Right AN Fittings for Your DIY Auto Repair | AlloyWorks Guide

Apr 18, 2025 OFFICIAL AlloyWorks Store I Radiators & Auto Parts

Whether you’re upgrading your fuel lines, oil system, or coolant setup, AN fittings are a crucial component for reliable and high-performance plumbing in your vehicle. At AlloyWorks, we offer a wide range of AN fittings built for durability and a leak-free seal – perfect for DIYers and performance enthusiasts alike.

But with so many sizes and configurations, how do you choose the right one? Let’s break it down.

🔧 What Are AN Fittings?

“AN” stands for Army-Navy, referring to a standardized sizing system originally developed for military specifications. Today, it’s a common sizing convention for automotive and aerospace plumbing.

Each AN fitting is identified by a dash number (like -6AN, -8AN, etc.) that refers to the inside diameter (ID) of the hose or tubing it connects to, measured in 1/16-inch increments.

✅ How to Select the Correct AN Fitting Size

Here’s a quick guide to help you choose the right AN fitting:

Know Your Hose ID: Match the AN fitting size to the inside diameter (ID) of the hose you’re using.
Determine Thread Type: Be sure to distinguish between male and female ends and whether you’re connecting to NPT, ORB, or another port style.
Consider Fluid Type and Flow Rate: Higher flow applications (like fuel return lines or coolant bypass) may require larger fittings (e.g., -10AN or -12AN).
Measure Twice: Use a caliper or thread gauge to confirm thread size if you’re replacing or adapting existing fittings.

📏 AN Fitting Size Chart

Here’s a reference chart that breaks down common AN fitting sizes, including hose ID and thread specifications:

AN Size	Dash Size	Hose ID (inches)	Thread Size (inches)	Port Gender
AN-2	-2	1/8"	5/16-24 UNF	Male/Female
AN-3	-3	3/16"	3/8-24 UNF	Male/Female
AN-4	-4	1/4"	7/16-20 UNF	Male/Female
AN-5	-5	5/16"	1/2-20 UNF	Male/Female
AN-6	-6	3/8"	9/16-18 UNF	Male/Female
AN-8	-8	1/2"	3/4-16 UNF	Male/Female
AN-10	-10	5/8"	7/8-14 UNF	Male/Female
AN-12	-12	3/4"	1-1/16-12 UN	Male/Female
AN-16	-16	1"	1-5/16-12 UN	Male/Female
AN-20	-20	1-1/4"	1-5/8-12 UN	Male/Female

🧠 Tips & Tricks for DIYers

Use AN Wrenches: These aluminum wrenches prevent scratching and damaging the anodized finish of the fittings.
Lubricate Threads: A small amount of anti-seize or assembly lube can prevent galling and ensure a proper seal.
Pressure-Test the System: Always test your setup before final assembly, especially in fuel and oil lines.
Tighten with Feel, Not Force: AN fittings are designed to seal with moderate torque. Over-tightening can cause leaks or crack the fitting.

⚠️ Common Mistakes to Avoid

Mixing NPT with AN Threads: They are not interchangeable. NPT is tapered; AN is straight. Use appropriate adapters.
Wrong Hose Size: Even a small mismatch can cause leaks or reduce performance. Always match hose ID with fitting size.
Cross-Threading: Easy to do if you're in a hurry. Always hand-tighten first to avoid stripping the threads.

🚗 Why Choose AlloyWorks AN Fittings?

At AlloyWorks, we use high-quality aluminum alloy to ensure our AN fittings are lightweight, corrosion-resistant, and capable of handling high-pressure performance setups. Whether you're building a fuel system, installing a catch can, or upgrading your cooling lines — we’ve got the right fit for your project.

Ready to Build?

Shop our full collection of AN fittings now and take your DIY auto repair to the next level.

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