2 AN Size
1/8 Metal Tube O.D.
5/16-24 SAE Thread size

3 AN Size
3/16 Metal Tube O.D.
3/8-24 SAE Thread size

4 AN Size
1/4 Metal Tube O.D.
7/16–20 SAE Thread size

5 AN Size
5/16 Metal Tube O.D.
1/2-20 SAE  Thread size
"AN" (Army-Navy)
Sizes were established with the help of the Aerospace industry years ago and were designated as the O.D. for size based on that AN Fitting it would be used with.
AN sizes
16 AN Size
1 Metal Tube O.D.
1-5/16-12 SAE Thread size

20 AN Size

1-1/4 Metal Tube O.D.
1/5/8-12 SAE Thread size

24 AN Size
1-1/2 Metal Tube O.D.
1-7/8-12 SAE Thread size

28 AN Size
1-3/4 Metal Tube O.D.
2-1/4-12 SAE Thread size

6 AN Size
3/8 Metal Tube O.D.
9/16-18 SAE Thread size

8 AN Size
1/2 Metal Tube O.D.
3/4-16 SAE Thread size

10 AN Size
5/8 Metal Tube O.D.
7/8-14 SAE Thread size

12 AN Size
3/4 Metal Tube O.D.
1-1/16-12 SAE Thread size
32 AN Size
2 Metal Tube O.D.
2-1/2-12 SAE Thread size

In order to plumb your vehicle with a minimum amount of time, effort and money, you should know the basics about hose, hose ends and adapter fittings. Hose diameters are assigned AN numbers. Using your automotive hose size, choose from the chart below to find the AN equivalent for hose, hose ends and adapter fittings. For example: a 3/8" standard hose equals -6 AN.
Help from Holley!

Typically, at wide open throttle, full power, an engine requires 0.5 lbs. of fuel
per horsepower every hour. A gallon of gasoline weighs approximately 6 lbs.
Therefore an engine rated at 350 horsepower will require about 175 pounds
(29 gallons) of fuel every hour.
(350HP x .5 lbs = 175 lbs of fuel
175 lbs/6 lbs = 29 gallons per hour)


The relationship of pressure to volume is inversely proportional. That is, as
pressure increases the volume will decrease, everything else being equal. A
certain amount of fuel pressure is always required to maintain engine performance
by assuring that fuel is available on demand. Also, other factors
and conditions must be taken into account such as acceleration G-forces and
friction within the fuel system itself. At the same time,however, an adequate
fuel volume is needed to ensure that the proper amount of fuel can always
flow to the engine, especially during peak demand situations. A basic understanding
of this critical pressure/volume relationship is needed when designing
the proper fuel supply system for your vehicle.

The fuel line system should be routed to avoid running near hot spots, such as
various exhaust system components, and designed to promote maximum fuel
flow. Most factory stock fuel systems utilize 5/16" fuel lines. This size works
well on street applications with stock engines. When the horsepower requirements
go up, however, the inadequacy of this line size soon becomes apparent.
A #6 (3/8") line size is sufficient for all street performance applications
and some racing applications. #8 (1/2") fuel lines are used on everything
else, including alcohol applications. Avoid using rubber fuel lines, or use
them sparingly, for two reasons. First, rubber is more resistant to the flow of
fuel than any hard line. An actual pressure loss can be measured over distance.
Second, for safety’s sake, it’s not a good idea to use rubber fuel line,
especially when using a high pressure performance fuel pump.

Like the fuel line, fuel line fittings are also a very important element in the total
fuel line system and should not be overlooked. Obviously, the fittings should
be the same size as the fuel line. Also, if at all possible, you want to minimize
the use of 90° fittings. Avoid sharp turns or bends in the fuel line routing;
these cause undue restrictions to the flow of fuel.

Do You Know How Much Fuel Your Engine/Nitrous System Needs?
To help figure out the size of fuel pump needed
for a given application, we have supplied a
formula for you.
Your pump must be capable of maintaining the
minimum GPH at working pressure under all conditions

HP divided by 2 = lb./hr. (pounds per hour)
lb./hr divided by 6 = gallons per hour required (min)
Multiply GPH by 1.15 for safety factor
Example: 600 HP divided by 2 = 300,
300 divided by 6 = 50
50 multiplied by 1.15 = 57.5 (minimum gallons per hour)
(This formula is for gasoline only.)
N.P.T. (National Pipe Threads). National
Pipe Threads are the next most popular thread size used in “Competition Plumbing.” You can find a resemblance between the size call outs and the I.D. (inside diameter) of the fitting.