We answer all (or most) of your -AN questions.
Dash sizes, or AN sizes, were first used in military applications, on aircraft, ships, etc., for hydraulic, fuel and coolant plumbing. The tough, braided/reinforced hose, coupled with threaded connections that were reliable in combat conditions, led early racers to buy military surplus hose, hose ends and fittings in the years following WWII and the Korean War. The racing community quickly made this type of plumbing popular, resulting in common use in today's performance and racing markets. The term AN (a common abbreviation for Army/Navy specification) sticks with us to this day. That's why the reinforced hose/hose end assemblies we see today are referred to as AN assemblies. So, we refer to these hoses, hose ends and fittings sizes with the word (or symbol) dash, or by the term AN, or by the term -AN. It all means the same thing. For example, "I'm plumbing my fuel system with dash 6 hose" or "I used dash 8 AN hose for my carburetor feed." When in written form, the dash symbol (-) or the word dash might be used. -AN (ARMY/NAVY) hose sizing is based on single and double-digit identification numbers. Common sizes for performance automotive applications include -3, -4, -6, -8, -10, -12, -16 and -20 (the larger the number, the larger the hose diameter). -3 and -4 sizes are typically used for brake line applications, small oil lines, some small fuel line applications, pressure gauges and vacuum lines. -6 size is typically applicable for fuel and oil plumbing -8 size is typically used for fuel, coolant and oil plumbing -10 size is typically used for oil, fuel or heater hose plumbing -12 size is typically used for coolant, large fuel delivery or dry-sump oil -16 size is typically used for coolant, dry-sump oil or large fuel delivery -20 size is typically used for coolant (radiator hose) What do these AN dash numbers really represent? Actually, there is a logical reason for these numbers, which otherwise might seem like made-up codes. The dash number refers to the hose inside diameter, in denominations of 1/16" of an inch. For example, a -10 size translates to 10/16", or 5/8" inside diameter. This is an easy way to understand dash sizes. Just think in terms of 1/16" increments. A -6 means that the inside diameter is 6/16" (or 3/8"). A -8 size is 8/16" (or 1/2") inside diameter. Just remember that the format is based on 1/16". Not to make things confusing, but those 1/16" increments are "nominal" numbers that indicate the O.D. of the hose end's internal metal tube (this tube slips into the hose). In reality, most AN hose makers actually make their hoses a bit on the tight-tolerance side, to the tune of about 1/32" smaller than the theoretical nominal diameter size, which aids in hose sealing onto the hose end's tube. So, a -6 hose, which theoretically should have an inside diameter of 6/16" (3/8" or 12/32"), actually has an inside diameter of 11/32". Nevertheless, using the 1/16" theory as your guide will help you to easily visualize what the inside diameter will be. For example, a -6 hose will provide about a 3/8" I.D. and a -8 hose will provide about a 1/2" I.D. If you've decided that your fuel line should feature a 1/2" inside diameter, you know that a -8 AN size will be the correct choice. (NOTE: The above sizes are based on Russell hose. Outside diameters may vary among hose manufacturers and among hose materials. Operating pressure ratings will vary depending on the specific type of hose construction). The "standard" of the AN hose world, at least for automotive performance applications, is a red and blue anodized finish. Although aluminum fittings and adapters are usually solid blue (sometimes red), two-piece hose ends are generally blue and red. Color shades, as well as finish gloss, will vary among makers, with items also offered in black or clear anodized finishes as well. So, if it's important to you that everything looks matched, it's best to stick with one particular manufacturer's hose ends and fittings. Remember: Anodizing is not a "coating." It's actually a controlled oxidation process that is used to protect the finish of an alloy, to allow the use of a color dye and/or to harden the alloy surface. A dull, non-gloss appearance is actually quite normal. If a higher gloss is desired, manufacturers can polish the aluminum beforehand, and they even have the option of using a gloss clear anodizing. The point is to look at the various makers' offerings, and if appearance is critical, decide what color and finish you prefer. Then stick with that one manufacturer's hardware. Otherwise, if you mix it up, you'll have different shades of blues and reds and gloss and flat finishes under the hood. If it's a race car, function is most important. But if it's a show car or street rod, it'll look best if all pieces match. These samples from XRP feature a stunningly beautiful appearance, with rich color and satin gloss finish. HOSE ENDS Hose ends attach directly to the hose and provide a high pressure seal. The hose end features a two-piece arrangement consisting of a socket (this slips over the end of the hose and features a female threaded opening) and a male/female tube assembly. The male/female piece features a male threaded nipple that threads into the hose end socket. The female (exposed) end is then ready to thread onto a male fitting at the desired installation location. These components are called "hose ends" because they comprise the end of the hose. Note: Although this is the most common configuration, not all assembled hose ends feature female threads. Some makers offer special male threaded ends that fit into female fittings. Here's a lineup of common -AN hose ends, shown here simply for size comparison. From left, shown here is a -6, -8, -10, -12, -16 and a 45-degree -20. Here's the same lineup pf -6, -8, -10, -12, -16 and -20 hose ends, with a U.S. quarter in the foreground, just to give you a size reference. Hose ends not only allow hose connection and sealing, but because hose ends are available in various shapes, the selection of the hose end shape will allow you to obtain installed angles necessary for clearance and preferred routing. Hose ends are available in straight, 30-degree, 45-degree, 90-degree, 120-degree, 150-degree and even 180-degree shapes. With regard to angled hose ends, these are also offered in two basic "profiles," including standard profile and low profile. Standard profile hose ends feature a tube neck, while low profile hose ends feature a forged or machined neck that shortens the hose end's distance from the fitting connection to the bend. Low-profile versions are good choices where installation space is at a premium. Here's a 90-degree hose end in a standard profile (note the tubular neck). In this example, the red end (upper left in this picture) attaches and seals to the hose, in practical terms becoming an integral part of the hose. The blue end (lower right in this picture) features a female AN thread and 37-degree internal seat, which will attach onto a male AN fitting. (Photo courtesy Aeroquip) Here's a -16 straight hose end with the collar removed. Hose ends feature a nipple that inserts into the I.D. of the hose. Note the smooth bore in this hose end for unrestricted fluid flow. This is typical of all makers hose ends. The male threads on hose ends (to retain the hose end collar) are very fine. Even with a new hose end straight out of the box, make sure that the threads are clean and free of any contaminants. The anodizing helps to harden the aluminum surface, but you can still gall the threads if you don't pay attention. The inside of this hose end's collar shows the wide-spaced "coarse" threads on the hose side of the collar. These threads, or ridges, help to retain the hose. Shown here are three straight -AN hose ends and straight -AN to NPT adapters. From left: -6 straight hose end and -6 male to 3/8" NPT male straight adapter; -8 straight hose end with -8 male to 3/8" NPT male straight adapter; and -10 straight hose end with -8 male to 1/2" NPT male straight adapter. This simply illustrates how a -AN hose end attaches to a -AN adapter. The hose end pictured here features a female threaded port with a 37-degree female (concave) sealing seat. The adapter shown here features a male threaded -AN tip with a 37-degree male (convex) sealing seat. The two angled seats mate, creating the seal. All -AN connections obtain their seal by the mating of these angled seats (these angled seats are sometimes called cones). No additional sealing material is required, so there's no need to add thread tape or compound to the -AN threads. -AN seals at the cone seating. NPT (tapered pipe thread) always requires thread tape or compound. Straight -AN thread that does not feature an angled seat requires an O-ring for sealing.