How to Choose the Right AN Fitting for Your Fuel System

Quick answer

Choose AN fittings by size first, then by angle and material, then by hose compatibility. Match the AN dash number to your hose and component threads, pick the bend angle that clears nearby parts, and confirm the fitting is rated for fuel and the pressure your system sees. If you are unsure, buy one size up in angle adjustability and verify the flare and seal style before installation.

AN fittings are the plumbing backbone of a performance fuel system, and the wrong choice usually shows up as a leak, a kink, or a fitting that will not clear a manifold. This guide walks through the decisions in the order that matters: size, thread and seal style, angle, material, and hose compatibility.

You do not need a shelf full of spares. You need a short list of measurements and a clear idea of how the line will route. The tips below help you buy once, install cleanly, and avoid the common mismatch between AN hose, AN hose ends, and the ports on your pump, rail, or regulator.

Start With Size: AN Dash Numbers and Hose Matching

AN sizes are expressed as dash numbers, and the dash number refers to the nominal hose inside diameter in sixteenths of an inch. A 6 AN fitting is designed for 6 AN hose, which is nominally 3/8 inch inside diameter. The most common fuel system sizes are 6 AN for return lines and moderate feed lines, 8 AN for higher-flow feed lines, and 10 AN or larger for high-horsepower or long runs.

Size is not just about flow. A fitting that is too small for the pump outlet creates a restriction, while an oversized line adds weight, cost, and routing difficulty. Match the fitting to the hose you already plan to run, then confirm the port size on the pump, rail, or regulator. If the port is smaller than the line, an adapter is the correct fix, not a mismatched hose end.

• Measure the hose inside diameter before ordering; do not assume a part number matches your line.
• Keep feed and return sizes consistent along the whole run to avoid step changes.
• When in doubt, confirm the AN dash number on the component port, not just the hose.

Thread and Seal Style: AN Flare vs. NPT vs. O-Ring

AN fittings use a 37-degree flare seal, which is different from the 45-degree flare used in some plumbing and from NPT pipe threads that seal on the threads themselves. Mixing these styles without the right adapter is a common source of leaks. Before buying, identify whether the port on your fuel pump, rail, or regulator is AN flare, NPT, or an O-ring boss style.

Seal style also affects how you tighten the fitting. AN flare fittings seal on the flare face and should be snug, not over-torqued. NPT fittings rely on thread sealant and can crack a thin-walled housing if tightened too far. O-ring boss fittings use a captured O-ring and a jam nut, and they are common on modern fuel system components. The correct choice depends on the port, not on the fitting alone.

• Never force an AN flare fitting onto an NPT port; use the correct adapter.
• Use fuel-compatible sealant only where the thread style requires it.
• Inspect the flare face for nicks before installation; a damaged seat will leak.

Angle and Routing: Straight, 45, 90, or 60 Degrees

Angle choice is driven by routing, not by looks. Straight fittings work when the hose can leave the port without bending sharply. A 45-degree fitting eases a line around a corner, while a 90-degree fitting turns the line tight against a firewall or frame rail. A 60-degree fitting sits between those two and is useful when a 90-degree bend would put the hose into a nearby component.

Swivel hose ends let you aim the fitting after the hose is assembled, which makes tight routing easier. If you are building a line for the first time, a swivel design gives you a second chance to clock the angle correctly. Plan the route with the hose end in hand before you cut hose; a few minutes of mock-up prevents a wasted length.

• Mock up the route with the hose end before cutting hose to length.
• Use a swivel hose end when the final angle is hard to predict.
• Keep bends gentle; sharp angles can kink the hose and restrict flow.

Material, Finish, and Hose Compatibility

Most AN fittings are aluminum, which keeps weight down and is suitable for fuel systems. Anodized finishes add corrosion resistance and a consistent look, and matte black is a common choice for engine bays where a low-key appearance is preferred. Stainless steel fittings are heavier and more expensive but can be useful in high-vibration or high-heat areas where aluminum may not be the best long-term choice.

Hose compatibility is just as important as the fitting material. CPE hose and PTFE hose use different hose ends, and using the wrong combination can cause the hose to leak or the fitting to not seal. Confirm that the hose end is designed for the hose type you are running, and check the operating pressure and temperature range of both the hose and the fitting before installation.

• Match the hose end to the hose material: CPE and PTFE are not interchangeable.
• Anodized aluminum is a good default for most fuel systems.
• Check pressure and temperature ratings for the hose and fitting together.

Fitment Checks Before You Buy

Before ordering, confirm three things: the AN size, the port thread and seal style, and the clearance around the fitting. A fitting that threads correctly can still fail if it contacts a manifold, a belt, or a suspension component under movement. Measure the space around the port and consider whether a different angle or a banjo-style adapter would route the line more cleanly.

If a specification is not listed for a fitting, treat that as a decision limitation rather than guessing. Contact the seller or manufacturer with your port size, hose type, and routing constraints. A few minutes of confirmation is cheaper than a return and a second install.

• Measure port threads and seal style before ordering.
• Check clearance at full suspension and engine movement, not just at rest.
• Ask for missing specifications instead of assuming they match your setup.

Decision rules for choosing AN fittings

• Match the dash number to the hose: A 6 AN hose end fits 6 AN hose; an 8 AN hose end fits 8 AN hose. Confirm the inside diameter of your hose before ordering. If the hose and fitting dash numbers differ, the assembly will not seal.
• Identify the port seal style: AN flare, NPT, and O-ring boss ports each need a different fitting or adapter. Check the port on the pump, rail, or regulator before buying. The wrong seal style is the most common cause of a fuel leak at a new fitting.
• Choose the angle from the route, not the shelf: Straight, 45, 60, and 90-degree fittings solve different clearance problems. Mock up the line before cutting hose. A swivel hose end gives you adjustability when the final angle is uncertain.
• Confirm hose material compatibility: CPE and PTFE hose use different hose ends. The fitting must be designed for the hose you are running. Mismatched hose and hose end can leak or fail under pressure.
• Check pressure, temperature, and clearance: Verify the fitting and hose ratings for your fuel system, and check clearance at full suspension and engine movement. If a rating is not listed, ask before you buy rather than assuming.

Product facts that help the decision

• 60-Deg. 6 AN Swivel CPE Hose End: The DeatschWerks 60-Degree 6 AN Swivel CPE Hose End is a hose end fitting designed for 6 AN connections. It features a female flare swivel and a 60-degree bend, with an anodized matte black finish. The 60-degree bend and swivel design help route a 6 AN line around tight engine bay obstacles while letting you clock the angle after assembly. The CPE construction means it is intended for CPE hose, not PTFE.
• LS1/LS6 Fuel Rails: LS1/LS6 Fuel Rails with Crossover for Pontiac Firebird Formula/Trans Am 1998-2002, Chevrolet Camaro Z28 and Z28 SS 1998-2002, Corvette Z06 1997-2004, Cadillac CTS-V 2004, Pontiac GTO 2004 If you are plumbing an LS1 or LS6 fuel system, the rail inlet and outlet ports determine the AN size and angle you need at the rail. Confirming the rail application first prevents buying a fitting that does not match the port.

Who this AN fitting approach is for

Best for

• Enthusiasts building or upgrading a fuel system who need to match AN size, angle, and seal style correctly
• LS1/LS6 or similar engine swaps where rail and pump ports must be confirmed before ordering fittings
• Anyone routing a 6 AN or 8 AN line who wants a swivel hose end for easier clocking

Not for

• Stock fuel systems that use factory quick-connect lines and do not need AN plumbing
• Builders who have not confirmed port thread and seal style and are guessing at sizes
• Applications requiring stainless hard line or specialist motorsport plumbing beyond standard AN hose ends

Choosing the right AN fitting comes down to confirming size, seal style, angle, and hose compatibility before you order. Measure your ports, mock up the route, and pick a swivel hose end when the final angle is uncertain. If a specification is missing, ask rather than assume, and you will spend less time chasing leaks and more time driving.