The AN thread ensures bombproof connections

If someone woke you up at 3 a.m. and asked how many types of thread you could name right off the bat, you might rattle off a few names, or maybe even quite a few. But chances are, the AN thread wouldn’t be among them unless you’re deeply involved in motor sports. The AN thread isn’t exactly common knowledge outside certain circles, but it’s one of those special thread types with a rich history and very specific applications. If you’ve never encountered the AN thread in your career, that’s great—but if you ever do, we’re here to help explain what it’s all about.

What Is the Origin of the AN Thread?

You may not recognize the AN thread in this part of the world since it’s a very American thread. In fact, the letters “A” and “N” stand for Army Air Corps and Navy. During World War II, these two branches of the U.S. military developed the AN thread. Originally used in the aerospace industry, the AN thread has expanded well beyond its military roots over the years. Its uses now span industries far and wide.

Key Features of the AN Thread

The AN thread is a classic type of thread designed for fittings, specifically connectors for pipes. It’s commonly used in situations where a flexible hose needs to connect to a rigid pipe. One of the most popular types of fittings that use AN threads are flare fittings, which are designed for high-pressure, heavy-duty environments prone to vibrations. In a flared fitting, one end of the pipe is flared outward, while the other end is tapered. As the nut is tightened, the flared union with an AN thread forms a tight seal. The critical aspect here is the 37-degree cone angle of the AN thread.

Understanding AN Thread Sizes

Traditionally, AN thread fittings were made in red and blue to symbolize the collaboration between the Air Corps and the Navy. While this added a touch of color to the otherwise monochrome world of plumbing, modern fittings rarely include such distinctions anymore. Instead, sizing is where things get a little more intricate. Unlike other threads, AN threads are specified using dash sizes, which are denoted by a dash followed by a number. For example, you might encounter sizes like -2, -6, or -24. These numbers represent the outer diameter in increments of 1/16 of an inch. So, if you’re trying to identify an AN thread with an outer diameter of 5/8 inch, you’d multiply 5/8 by 16, which gives you 10. Thus, the AN thread with a 5/8-inch outer diameter would be designated as -10.

Challenges with Inner Diameter Measurements

It’s worth noting that the diameter specifications listed in AN thread charts refer to the outer diameter. This can lead to confusion when working with hoses or pipes, as the ratio of outer to inner diameter varies depending on the material and purpose of the pipe. To address this issue, a separate naming convention exists for AN threads, where the appropriate number is appended to the abbreviation “AN.” For instance, an AN6 thread will fit into an -6 AN thread, but their internal dimensions may differ slightly.

Applications of the AN Thread

Now, let’s talk about why you might need the AN thread. The AN thread remains a staple in the aerospace industry and various industrial sectors, particularly in the United States. Over here in Germany, you’re more likely to encounter AN threads in the automotive world, especially in motor sports. These threads are used in fluid circuits for their robust and reliable seals. Whether you’re looking for adapters, connectors, or hoses, AN-threaded parts are available in every imaginable configuration, shape, and color. In addition to the AN abbreviation, you’ll often see components labeled with a dash size, referring to the standardized sizes mentioned earlier.

Are There Alternatives to the AN Thread?

While the AN thread isn’t revolutionary, it does face competition, particularly in the motorsport arena. The AN thread shares identical dimensions with the SAE flare fittings, though there’s a catch. Even though the threads themselves are the same, the fittings aren’t. AN fittings feature a 37-degree flare angle, whereas SAE fittings use a 45-degree angle. Combining components from both can compromise the integrity of the connection. Another close cousin of the AN thread is the JIC flare fitting, which also operates at a 37-degree angle. These threads are interchangeable with AN threads and can be used together. However, combining components from different standards—even if they fit perfectly—can sometimes violate regulations, especially in sensitive fields like aviation. If you’ve ever seen thread tables listing JIC and AN threads as identical, now you understand why.

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