If you're working on a fuel system, cooling line, power steering setup, or any fluid transfer project, you may encounter two different pipe connection standards that need to join together. An adapter fitting bridges that gap. The EVIL ENERGY 6AN Male Flare to 3/8" NPT Pipe Fitting Adapter is one solution designed for exactly this problem, but understanding when and how to use it matters more than the product itself.

What Are AN Flare and NPT Thread Standards?

AN (Army-Navy) flare fittings and NPT (National Pipe Taper) threads are two completely different ways to connect pipes and hoses. They're not compatible on their own, which is why adapters exist.

AN flare fittings use a cone-shaped seal. The EVIL ENERGY adapter uses a 37-degree angle on the flare side, which is the standard for automotive and high-performance fuel system work. You'll find these on performance car fuel lines, cooling systems, and custom builds.

NPT threads use a tapered pipe thread design with a 60-degree angle. These are common in household plumbing, industrial equipment, and many factory automotive applications. NPT threads seal by the thread itself, not by a separate cone seal.

Decoding the 6AN and 3/8" Specifications

The numbers in the product name tell you exactly what connections this adapter makes. The "6AN" refers to the AN flare side. In AN sizing, the number roughly corresponds to the hose inner diameter in sixteenths of an inch, so 6AN means the hose is approximately 6/16ths of an inch (or 3/8 inch) inside diameter. The thread size is 9/16-18 UNF, which you'll see printed on your existing fittings if you're replacing or connecting to them.

The "3/8 NPT" is the pipe thread size on the other end. NPT sizes are also given in fractions of an inch. When you're looking for the right adapter, measure your existing connections or check what size threads are already on your equipment. Mismatching sizes is the most common mistake—a 6AN adapter won't work with a 4AN hose, and a 3/8" NPT thread won't fit a 1/2" NPT port.

Material and Durability Considerations

The EVIL ENERGY adapter is made from aluminum alloy 6061-T6, which is lightweight and corrosion-resistant. The anodized black surface adds an extra protective layer. Aluminum is standard for this type of fitting because it's strong enough for fluid pressure but won't rust or corrode like steel can.

Aluminum fittings are fine for fuel, coolant, power steering fluid, and most automotive applications. If you're using this in an extremely corrosive environment, stainless steel alternatives exist, but they're less common for casual projects.

Installation and Sealing Requirements

Getting the seal right is critical. The AN flare side seals itself through the 37-degree cone—when you tighten the fitting, the cone seats properly and creates a leak-free connection. This is why you need the right hose end or fitting to match.

The NPT thread side is different. NPT threads alone don't seal perfectly. EVIL ENERGY specifically recommends using sealant or PTFE tape on the NPT end to prevent leaks. PTFE tape (also called plumber's tape or Teflon tape) is inexpensive and easy to apply—wrap it around the male threads a few times before screwing the fitting in. Some people prefer pipe thread sealant compound instead. Either approach works, but don't skip this step if you want a reliable connection.

When you install the fitting, use two wrenches if possible—one to hold the adapter body and one to turn the nut. This prevents twisting the fitting and breaking the seal.

Common Applications and When You Need This Adapter

Custom fuel systems often mix AN fittings with factory NPT ports. Classic car restorations, performance engine builds, and modified cooling systems frequently need these adapters. Power steering upgrades also use them.

The EVIL ENERGY 6AN to 3/8" NPT adapter comes as a two-piece set, so you have a spare or can use both on the same project if needed. Before ordering, verify your hose size (6AN) and your thread port size (3/8" NPT) by checking the existing fittings or looking at your system's documentation.

The product in this guide: EVIL ENERGY 6AN Male Flare to 3/8" NPT Pipe Fitting Adapter Aluminum Straight Black 2PCS