AN Fitting & Hose Size Chart: Dash Sizes, Threads, and How to Choose

Dash sizes, thread sizes, hose types, and how AN compares to NPT, ORB, and JIC

AN fittings show up on just about every serious build: fuel systems, oil coolers, turbo feeds and drains, transmission lines, and breathers. The sizing system is simple once you know the rule behind it, but the mix of dash sizes, thread callouts, and port types trips up a lot of people. This guide puts everything in one place so you can identify what you have and order the right parts the first time.

If you are ready to build lines, our step-by-step guide covers it: How to Install AN Hose Ends.

What the Dash Number Means

The dash number is the size of the line in sixteenths of an inch, measured on the outside diameter of the matching hard tube. A -6AN fitting is sized for 6/16", or 3/8", OD tube. A -8AN is 8/16", or 1/2". A -10AN is 10/16", or 5/8".

Hose is sized to match. The inside diameter of a -6AN hose is close to the inside diameter of 3/8" tube, so a hose and a hard line of the same dash size flow about the same. The actual hose ID varies by hose type and manufacturer, which is why the chart below lists hose ID as typical rather than fixed.

The dash number does not describe the thread size. Each dash size has its own thread, listed below.

AN Size Chart

*Typical ID for rubber-lined braided hose. PTFE-lined hose usually runs slightly smaller for the same dash size. Nominal dimensions; tolerances apply. Check the product page for the hose you are using.

How to Identify a Fitting You Already Have

If you are replacing or adapting an existing line, measure the thread rather than guessing from the hose.

• Male threads: Measure across the outside of the threads with calipers. A -6AN male reads just under 0.563" (9/16"), a -8AN just under 0.750" (3/4").
• Female threads: Measure across the inside of the threads. The reading will be a little smaller than the thread size, so match it to the closest size in the chart.
• Confirm the pitch: A thread pitch gauge settles it. -6AN is 18 threads per inch, -8AN is 16, -10AN is 14.
• Look at the seat: AN fittings have a 37° cone-shaped flare. If it looks noticeably shallower or there is no cone at all, it may be a 45° SAE flare, a pipe thread, or an O-ring port (see below).

Choosing a Hose Type

The hose matters as much as the fitting. The liner decides what fluids and pressures the line can handle, and the hose end has to match the hose construction.

Ratings shown are for our hoses. Pressure ratings drop as hose size goes up, so check the size you are using below. Other brands rate their hoses differently.

Operating Pressure by Size

• Rubber-lined hose is easy to assemble and flexible, and it is the go-to for most fuel, oil, and coolant lines. Over time some fuel vapor can permeate the liner, which is why a car with rubber-lined fuel lines may smell like fuel in a closed garage.
• PTFE-lined hose stops vapor permeation, handles much higher pressure and heat, and is the correct choice for power steering and other hydraulic-style lines. It is stiffer, has a larger bend radius, and requires PTFE-specific hose ends.
• Hose ends are not interchangeable between the two. Rubber-lined hose ends grip the liner with a threaded socket and nipple. PTFE hose ends use a compression olive that seals against the PTFE liner. Use PTFE hose ends with PTFE hose only.

Our AN fittings and flexible race hoses are not for use in brake systems. Our race hoses are also not for A/C lines or in-tank use where the hose stays submerged in fuel or oil.

AN vs. JIC vs. NPT vs. ORB

Most leaks and stripped threads on new builds come from mixing up these four. Here is how they differ.

• AN: Straight threads with a 37° flare. The seal happens metal-to-metal at the flare, not at the threads, so AN connections do not use thread sealant or tape.
• JIC: Uses the same 37° flare and the same thread sizes as AN, so the two will connect. AN fittings were developed to a military specification with tighter tolerances and a stronger thread form, while JIC is the industrial equivalent. For automotive fuel, oil, and coolant work, they are commonly used together.
• 45° SAE flare: Looks similar to AN, and several sizes share the same thread, but the angle is different. A 45° fitting will thread onto a 37° fitting and leak. Do not mix them.
• NPT (pipe thread): Tapered threads that seal by wedging together, so they need thread sealant. NPT sizes are based on pipe, not tube, so a 1/4" NPT port is much larger than 1/4" tube. Apply sealant only to the pipe threads, never to an AN flare, and keep it off the first thread so it doesn't end up in the system.
• ORB (O-ring boss): Straight threads that seal with an O-ring at the base of the fitting. ORB ports use the same thread sizes as AN by dash number (a -8 ORB port is 3/4"-16), which is why they are easy to confuse. No sealant needed; just lube the O-ring. Common on fuel pumps, filters, and transmissions.

Matching NPT Ports to AN Sizes

When adapting from a pipe-thread port, this is the closest AN size for each NPT size.

Adapters are available up or down a size as well, but going to a much smaller AN size than the port creates a restriction at the fitting.

A Short History of AN Fittings

"AN" stands for Army-Navy. The standard came out of the World War II era, when the U.S. military needed hydraulic and fuel line fittings for aircraft that were interchangeable no matter which supplier made them. The 37° flare and straight-thread design held up to high pressure and vibration and could be taken apart and reassembled without wearing out.

Those same qualities are why the racing world adopted AN fittings. Lightweight aluminum fittings, braided hose, and a repeatable seal made them the standard for fuel, oil, and coolant plumbing in motorsports, and that carried over to street performance builds. Industrial JIC fittings grew out of the same design, which is why the two share a flare angle and thread sizes today.

Common Mistakes to Avoid

• Tape or sealant on AN flares. It keeps the flare from seating and can break loose into the fuel or oil system.
• Mixing 37° and 45° flares. They thread together and still leak.
• Over-tightening aluminum. AN fittings seal at the flare. Cranking down on them distorts the flare and damages the threads. Snug to spec and stop.
• Using an adjustable wrench. It slips and chews up anodized hex flats. Use an AN wrench or a properly sized open-end wrench.
• Using rubber-hose ends on PTFE hose (or the reverse). The sealing methods are completely different.
• Sizing by port instead of flow. A large port with a small adapter becomes the restriction in the system.

Shop AN Fittings and Hose

We carry AN fittings, adapters, hose ends, and flexible race hose in -3AN through -20AN, CNC machined from 6061 aluminum with a black hard anodized finish. When you are ready to build your lines, follow our step-by-step AN hose end installation guide.

If you are not sure which size or adapter you need, email us at sales@aceraceparts.com with what you are connecting and we are happy to help.