AN Hardline Fittings

Q: Do I need a flaring tool to install hardline fittings?

It depends on which style you choose. The AN hardline tube nut and sleeve is a flare style fitting, so the tube end must be flared to 37° with a flaring tool before the nut is threaded on. The AN to hardline compression fitting does not require flaring at all, a brass ferrule compresses around the tube as the fitting is tightened, so it is the more practical choice for a home garage without a flaring tool. Either way, a tube cutter for a square cut is worth having on hand.

Q: Can hardline fittings be mixed with braided or PTFE hose in the same fuel system?

Yes. Both the flare style and compression style hardline fittings terminate at the same 37° AN seat used by braided and PTFE hose ends, so a builder can run rigid hardline through a frame rail or trunk floor and switch to flexible hose near the engine or fuel rail where movement and heat cycling call for it. This mixed approach is common on LS swaps and EFI conversions where routing space is tight.

Braided AN hose flexes into place, but the moment a fuel system calls for rigid tube, a hose end will not seal it. Evil Energy AN hardline fittings convert a 37° AN thread into a secure termination point for aluminum or stainless steel hardline tubing, so a custom fuel line, from tank to rail, can run on clean, vibration resistant hard line instead of an unbroken run of hose.

AN Hardline Tube Adapters: Flare or Compression

Rigid tube does not seal the way hose does, and that mismatch is where most DIY leaks start. Evil Energy carries both connection methods used on OEM and race fuel systems, so the choice comes down to the tools already in your box. The AN hardline tube nut and sleeve uses a 37° flare: the tube end itself is flared with a 37° flaring tool, then the nut draws it into the AN seat, the same method used on factory hard lines. The AN to hardline compression fitting skips flaring altogether: a brass ferrule compresses around the tube inside the fitting body, giving builders without a flaring tool a genuine 37° AN seal on aluminum or stainless steel line.

AN Size to Hardline OD Reference

AN Size	Thread	Hardline OD
3AN	3/8-24 UNF	3/16 in
4AN	7/16-20 UNF	1/4 in
6AN	9/16-18 UNF	3/8 in
8AN	3/4-16 UNF	1/2 in
10AN	7/8-14 UNF	5/8 in
12AN	1 1/16-12 UNF	3/4 in
16AN	—	1 in

Sized for LS Swaps, EFI Conversions and Tight Engine Bay Routing

From a 3AN feed line on a small block swap to a 10AN return line on a high output EFI system, Evil Energy hardline fittings are machined from aluminum alloy with a brass ferrule or sleeve and finished in black to blend into an engine bay. Because both the flare and compression styles thread onto the same 37° AN seat, they mix freely with the AN fittings already in your system, so a hard mounted section near the frame rail and a flexible PTFE fuel line near the engine can share one continuous, pressure tested circuit. Measure the hardline outside diameter before ordering, cut the tube square, and deburr both edges; that single step decides whether a hardline joint holds fuel pressure for years or weeps at the first heat cycle.

Paired with the rest of our fuel line fittings, these AN hardline fittings give a weekend LS swap or a fully custom EFI fuel system a repeatable way to join tube to AN, size for size, without redesigning the rest of the line.

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FAQs about AN Hardline Fittings

Does hardline tubing need different fittings than AN hose?

Yes. A standard AN hose end is built to grip a hose cover, it is not designed to seal against rigid tube. To connect hardline tubing into a 37° AN system you need either an AN hardline tube nut and sleeve or an AN to hardline compression fitting. Both create the same 37° AN flare seal, the difference is only in how the tube end is prepared, flared versus compressed.

How do I know what size hardline fitting to order?

Measure the hardline outside diameter (OD) with calipers before ordering, do not go by AN size alone since the same AN thread can pair with more than one tube OD depending on the fitting. As a quick reference: 3AN fits 3/16 in tube, 4AN fits 1/4 in, 6AN fits 3/8 in, 8AN fits 1/2 in, 10AN fits 5/8 in, 12AN fits 3/4 in, and 16AN fits 1 in tubing. Also confirm the AN thread size matches whatever it is threading into on the rest of the fuel system.

Do I need a flaring tool to install hardline fittings?

It depends on which style you choose. The AN hardline tube nut and sleeve is a flare style fitting, so the tube end must be flared to 37° with a flaring tool before the nut is threaded on. The AN to hardline compression fitting does not require flaring at all, a brass ferrule compresses around the tube as the fitting is tightened, so it is the more practical choice for a home garage without a flaring tool. Either way, a tube cutter for a square cut is worth having on hand.

How do I get a leak free seal on a hardline connection?

Cut the tube square and deburr both the inside and outside edge, a rough or angled cut is the most common cause of a hardline leak. Assemble the parts in the correct order (nut, then sleeve or ferrule), start the threads by hand to avoid cross threading, then tighten until snug and true, over tightening an aluminum fitting can distort the seal instead of improving it. Pressure test the completed line before startup so any weep shows up on a bench, not on the road.

Can hardline fittings be mixed with braided or PTFE hose in the same fuel system?

Yes. Both the flare style and compression style hardline fittings terminate at the same 37° AN seat used by braided and PTFE hose ends, so a builder can run rigid hardline through a frame rail or trunk floor and switch to flexible hose near the engine or fuel rail where movement and heat cycling call for it. This mixed approach is common on LS swaps and EFI conversions where routing space is tight.

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AN Hardline Fittings

AN Hardline Tube Adapters: Flare or Compression

AN Size to Hardline OD Reference

Sized for LS Swaps, EFI Conversions and Tight Engine Bay Routing

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