AN to AN with NPT Fittings

No. AN threads are straight (UNF thread form) and seal on a 37° flare seat. NPT threads are tapered and seal by thread deformation combined with sealant. The thread pitch, angle, and profile are different enough that forcing an AN male into an NPT female port results in at most one or two partial threads of engagement before the fitting bottoms out or cross-threads. That connection will leak fuel under pressure — sometimes immediately, sometimes after a few heat cycles when the minimal thread engagement relaxes. Always use a purpose-built AN to NPT adapter fitting that provides the 37° AN flare seat on one side and the correct NPT taper on the other. The two sealing mechanisms must stay on their respective sides of the same adapter. If you are unsure which NPT size your component uses, measure the port opening diameter: 1/8 NPT measures approximately 0.405 inch at the major diameter, 1/4 NPT approximately 0.540 inch, and 3/8 NPT approximately 0.675 inch. None of these correspond to the nominal pipe size number.

On the NPT side, use a fuel-rated PTFE tape — specifically yellow gas-line tape, not standard white plumbing tape — or a fuel-resistant liquid thread sealant such as Permatex High Performance Thread Sealant or Loctite 567. Apply 3 to 4 wraps of tape in the same direction as the threads (clockwise when looking at the male end), keeping the first one or two threads clean to prevent tape shreds from entering the fuel system. If using liquid sealant, apply a thin bead into the thread roots and wipe away excess after installation. On the AN flare side, do not apply any sealant, tape, or paste. The 37° metal-to-metal flare seat is a dry seal. Any foreign material between the flare surfaces prevents proper seating, reduces the effective contact area, and creates a leak path that tightening harder will not fix.

Most aftermarket fuel system components use one of four NPT sizes, and matching the wrong size is the fastest way to damage a port:

1/8 NPT — mechanical fuel pressure gauge ports, boost reference ports on regulators, small bleed ports, and some coolant temperature sensor bosses. Least common in main fuel flow paths.

• 1/4 NPT — carburetor fuel inlet fittings, some fuel pressure regulator return ports, smaller distribution blocks, and older mechanical fuel pump inlets. Also used on some fuel filter housings.
• 3/8 NPT — the most common size for electric fuel pump inlet and outlet ports (especially 255 LPH and 300 LPH external pumps), EFI fuel pressure regulator main ports, standard fuel filter housings, and Y-block distribution fittings. If you are plumbing a typical EFI return system, at least two of your connections will likely be 3/8 NPT.
• 1/2 NPT — high-flow pumps rated above 400 LPH, large fuel distribution manifolds, surge tank plumbing, and some diesel lift pump ports. Overkill for most street performance applications below 600 HP unless the pump manufacturer specifies it.

Before ordering, check your component's spec sheet or measure the port. Do not guess based on visual size alone — 1/4 NPT and 3/8 NPT look similar to the naked eye but differ by 0.135 inch at the major diameter.

Yes. 6061-T6 aluminum with a black anodized finish is fully compatible with pump gasoline (87–93 octane), diesel, E10 through E85 ethanol blends, and most racing fuels. The anodizing process creates a hard aluminum oxide layer that resists corrosion from ethanol, moisture, and fuel additives. Evil Energy fittings are anodized after CNC machining, so the entire surface — external and internal bore — carries the corrosion protection. However, if you are running straight methanol (M1) as a primary fuel, aluminum is not the correct material long-term. Methanol is more aggressive on aluminum oxide than ethanol, and stainless steel fittings are the safer choice for dedicated methanol systems. For everything else in a typical street or street-strip build — pump gas, E85, diesel — 6061-T6 aluminum with a quality anodized finish is the industry standard and will not degrade from fuel exposure.

Three scenarios cause the majority of NPT adapter leaks in confined installations, and each has a specific fix:

Cross-threading from poor visibility. When you cannot see the port straight-on, start the fitting by hand and rotate it counterclockwise until you feel the thread drop into alignment, then tighten clockwise. This prevents the male NPT from entering at an angle that cross-threads the first few threads before you feel resistance.

Inadequate sealant coverage in a port you cannot inspect. Liquid thread sealant is often more reliable than tape in tight spaces because it flows into the thread roots uniformly and you can visually confirm coverage by seeing excess squeeze-out around the fitting hex after tightening. Tape can bunch up or skip threads when you cannot see what you are doing.

Overtightening to compensate for a bad angle or insufficient sealant. Aluminum NPT threads will permanently deform if you exceed roughly 15 to 20 ft-lbs for a 3/8 NPT fitting. If it leaks at proper torque, back it out, inspect the threads for damage, clean the port, reapply sealant, and reinstall. If clearance is the root cause — the port faces a frame rail, header tube, or body panel — a 45° or 90° AN to NPT adapter redirects the AN connection away from the obstruction while keeping a straight and properly aligned shot into the NPT port. See our full NPT fittings range for additional angle options at Evil Energy NPT fittings. If the leak persists after correct installation, the NPT port itself may be worn from repeated use — in that case, a thread sealant with gap-filling properties like Loctite 567 handles worn threads better than tape alone.