A Guide to AN Hose and Fittings

Havoc Speed carries the Fragola Performance brand. This post is a mix of official/unofficial terminology we we use in house and with our customers.

This guide is meant to help you find what you need, in one consolidated location. Some customers say they’re intimidated to come in to the store without knowing the lingo, terms, or sizes. Instead they try to figure it out online, often purchasing the wrong items. We’ve collected many common questions we’re asked, and hope to answer them here.

Origin of the AN Fitting

The AN fitting is a US military created specification that dates back to World War II and is the agreed upon standard between the Army and Navy, hence “AN”. It’s used to connect flexible hoses and tubing that carry fluid.

In this post we’ll be using the following terms listed below. There are other terms used for the same items in different areas and by different manufacturers, these are the terms we use, they’re universal and any shop or parts supplier will know what you’re talking about.

Definitions

  • AN: Army/Navy
  • ORB: O-Ring Boss
  • PTFE: Polytetrafluoroethylene
  • NPT: National Pipe Thread
  • BSPT: British Standard Pipe Thread
  • Hose End: Any fitting that attaches directly to a hose
  • Union: Male/Male Fitting of the same size
  • Coupler: Female/Female fitting of the same size
  • Adapter: Anything that adapts or connects two different sizes or types of fittings
  • JIC: Industrial terminology for 37 degree AN fittings
  • IF: Inverted Flare
  • IFF: Inverted Flare Female
  • IFM: Inverted Flare Male
  • Bulkhead: A fitting that that passes a connection through a wall, panel, or tank.

Types of Fittings

  • Hose Ends: Any fitting that attaches directly to a hose, no matter the style of hose, or type of connection, if it attaches directly on to a hose, we will always call it a hose end.
    AN Hose End Fittings
  • Unions: A male/male fitting of the same size that connects two female threaded fittings together. Will always have the same connection on each end, anything different is an adapter, and anything with female ends is a coupler.
    AN Male/Male Union
  • Couplers: A female/female fitting of the same size that connects two male fittings together. Will always have the same connection on each end, anything different is an adapter.
    AN Female/Female Coupler
  • Adapters: Anything that adapts or connects two different sizes or types of fittings together.
    AN Adapter Fittings
  • Bulkhead: One of the best ways to pass fuel, brake, or other lines through a tank or firewall is with a bulkhead fitting. They can be used with either rigid hard line (bent and flared with a 37 degree flare tool) or used with hose ends on flexible hose. A bulkhead fitting is also a great place to transition from one type of line to another (rigid hard line to hose and hose end) to accommodate for engine vibration. Bulkhead fittings are a male/male union type fitting which has a longer thread (or two sets of threads) on one end. The extended thread is used for the securing nut, the other is for the sealing fitting. This is used to pass a connection through a firewall, floor, engine bay, tank, etc. The hole is cut, the fitting installed, a sealing/insulating washer typically installed, and a securing nut to secure the assembly. Hose with hose end or hard line with tube sleeves and nuts are then connected to each side. They’re available in straight, 45 degree, 90 degree, and tees. To purchase a bulkhead setup, you’ll need to order the fitting itself, the corresponding bulkhead nut and the matching sealing washers.
    AN Bulkhead Fitting
    AN Bulkhead Fitting
    AN Bulkhead Fitting
    AN Bulkhead Fitting
    AN Bulkhead Fitting
  • Y-Fittings: Splits or combines one hose or line into two. Available in common sizes and some transition sizes. 10AN single to dual 8AN, 8AN single to dual 6AN, etc.
    Fragola AN Y-Fittings
  • Tee Fittings: Used to tap or add to circuits. These are available in multiple configurations. We have these with male and female swivel combinations, as well as AN and NPT combinations.
    Fragola AN Tee Fitting
    Fragola AN Tee Fitting
    Fragola AN Tee Fitting
    Fragola AN Tee Fitting

Types of Threads and Sealing Methods

Fittings seal with either a tapered thread, a flare, or an o-ring/washer. Tapered threads (NPT pipe thread) seal on the tapered thread itself, and will require sealing tape or paste. Straight thread (metric and AN O-Ring) will seal with either a washer or o-ring. Or on a flare, either inverted or standard AN style. Do not use a washer or o-ring on a tapered thread, or fittings with flares, do not use sealing tape or paste on straight threads or flares.

  • Standard Flare Male AN: This is a straight thread that seals on the 37 degree flare. This is what majority of the hose ends and other female fittings will attach to. It’s the exact same thread as a straight ORB fitting, but seals on the flare instead of an o-ring. In a pinch, you could use an o-ring on this side and install like an ORB fitting. (EX: You could take a 6AN male flare fitting, put a 6AN ORB o-ring on it, and install in a port designed for a 6AN ORB fitting, the taper on the end may I obstruct flow if there’s movement from the port towards the fitting, from the fitting towards the port is usually fine.
    AN Flare Adapter
  • ORB (O-Ring Boss): We also call this AN O-Ring. AN O-Ring is a straight thread with the same thread size and pitch as a flared AN fitting or hose end but seals with an O-Ring instead of a flare.
    Fragola AN O-Ring Boss
  • NPT (National Pipe Thread): Tapered thread, seals with thread tape or paste. Typical with gauge senders, intake manifolds and older style fuel rails. Fragola Performance refers to these as “FPT” (Female Pipe Thread) and “MPT” (Male Pipe Thread). Customers often return these items, assuming we’ve sold them the wrong part. They ask for “NPT” and “FPT”/”MPT” is on the actual packaging. Pipe threads have some disadvantages, voids in the seal remain after installation making them prone to leakage. Because they seal with a metal to metal wedge, sealing tape or paste is required to fill these voids.
    Fragola NPT AN Adapter
    Tapered Thread Fitting Diagram
  • NPS (National Pipe Straight): This isn’t a fitting we are very involved with, we only carry a couple NPS fittings, and that’s the 1/4″ NPS to AN flare adapter used in some transmissions (mostly GM). NPS is the same thread angle, shape and pitch as NPT, both threads have a 60° included angle and have flat peaks and valleys. NPT threads are tapered and require sealing tape or paste, NPS threads are straight, and require a gasket or o-ring to create the seal. NPT and NPS threads will engage in either, but neither will seal in the others thread.
    AN to NPS Transmission Fitting Adapter

Types of Adapters

  • AN female/female (Different Sizes): Has a female flared AN thread on each side, and are different sizes. If these were the same size, they’d be a coupler.
    Fragola AN Female Female Adapter
  • AN male/male (Different Sizes): Has a male flared AN thread on each side, and are different sizes. If these were the same size, they’d be a union.
    Fragola AN Male Male Adapter
  • AN male/female (Different Sizes): Has a male AN flare thread in one size on one side and a female AN flare thread in another size on the other.
    Fragola AN Male Female Adapter
  • AN to Inverted Flare: Has a straight thread on one side that seals with an inverted flare at it’s base, and a male AN flare thread on the other side. No washers, o-rings or sealant are needed on these, they seal on the inverted flare.
    AN to Inverted Flare Adapter Fitting
  • AN flare to AN O-Ring: Has a male straight thread with AN flare on one side, and a male straight thread with no flare on the other. It seals with an ORB o-ring on the non-flare side. These can either have the same size or different sizes on either end.
    AN Flare to AN O-Ring Adapter Fitting
  • AN to NPT: This adapter has a male or female AN flare on one side and a tapered thread on the other. These are available in straight, 45 degree and 90 degree variations. Sealant or tape will be required on the tapered thread side.
    AN Female to NPT Adapter Fitting

    AN to NPT 45 Degree Adapter Fitting
    AN to NPT 90 Degree Adapter Fitting
  • AN to Tube Adapters: Has a male or female AN flare thread on one side and a female compression style connection on the other side. Used for transitioning from one style of connection to another. Many people use it to connect an AN hose to an OE factory hard fuel line where a spring lock connection cannot be utilized.
    AN to Tube Compression Adapter Fitting
    AN to Tube Compression Adapter Fitting
  • AN to NPS Adapters: Primarily used in transmission cooler ports, this is an NPS straight thread that seals with a washer on one side, and a male AN flare thread connection on the other side.
    AN to NPS Transmission Fitting Adapter
  • Carburetor and EFI Adapters: For connecting original or aftermarket carburetors, fuel rails, filters, lines and pumps to AN hoses and fittings.
    Fragola Carburetor Inlet Adapter Fittings
    AN to Spring Lock Fuel Line Adapter
    AN to Male Spring Lock Fuel Line Adapter
  • Hose Barb Adapters: Similar to push lock style hose ends but with a male AN flare thread on one side, and a corresponding barb on the other side. The size charts below correspond with these. A 4AN adapter will have a 1/4″ barb that fits 4AN push lock or any other rubber hose, the 6AN adapter will have a 3/8″ barb that fits 6AN push lock or any other rubber hose, the 8AN adapter will have a 1/2″ barb that fits 8AN push lock or any other rubber hose. These are useful for connecting stock rubber hoses and lines to AN fittings. Breathers, brake boosters, etc.
    Fragola AN to Hose Barb Adapter Fitting
  • Inline Gauge and Sensor Adapters: These are offered in several thread and size variations, but all of them will have a 1/8″ NPT port in the middle, you can use this port to screw in probes, sensors, or other fittings. Many use these as a source of fuel for wet nitrous kits and install them at the fuel rail hose connection. Some are AN male/male, some are AN male/female, and some are NPT to AN. We carry them in all sizes.
    Fragola AN Male to Female Inline Gauge Adapter Fitting
    Male to Male AN Gauge Adapter Fitting
    Inline AN to NPT Gauge Adapter Fitting
  • Metric Adapters: Converts male metric threads (that seal with a washer or o-ring) on one side to AN male flare thread on the other. We also offer these in swiveling 90 degree with male or female AN flare thread connection
    AN to Metric Adapter Fitting

Types of Hose

  • PTFE Hose: PTFE is short for Polytetrafluoroethylene (also known as it’s trademarked name Teflon™) In the performance world we use a stainless braided version of the hose with a PTFE liner instead of rubber, this hose is sometimes covered by a clear, smoked, or black covering. PTFE is rated to much higher pressure, it is impervious to ATF, brake fluid, nitrous, engine oil, methanol, ethanol, freon, etc. PTFE is the go to hose for hydraulic power steering, alcohol based fuel systems, or pressurized oil hoses. PTFE requires it’s own style hose end, and will always be prefaced with PTFE. PTFE hoses, like push lock, interchange with all other AN fittings, adapters, unions, etc.
    Fragola PTFE AN Hose
    “The fuel smell” AN hose vs. PTFE hose
    Standard AN hose (black or stainless pro-flow hose) is made from Chlorinated Polyethylene, and is compatible with all known fuels. The actual alcohol molecules are smaller than the pores of AN hose itself causing the smell of alcohol fuels to permeate the hose. It’s not hazardous, but it is possible that you will smell fuel in the garage, or in and around the car.
  • Standard “AN” Hose: This is your industry standard, braided AN hose. Fits Fragola “Pro-Flow” AN style hose ends. Will not fit push lock, or PTFE hose ends. Compatible with all hydrocarbon and alcohol based fuels along with synthetic and natural based lubricants. It’s a CPE (Chlorinated Polyethylene) synthetic rubber hose. It is sold with either a stainless braided external layer or a black nylon external layer.
  • Stainless braided AN hose has two layers of stainless braid, the inner layer to resist collapse and expansion, and the outer layer for abrasion resistance. 
  • Black nylon braided AN hose has one layer of stainless braid to resist collapse and expansion, and a nylon/fabric outer layer for abrasion resistance. Black nylon hose (in addition to looking better) won’t scratch things it comes in contact with.

Types of Hose Ends

  • Pro-Flow AN hose end: This is the industry standard AN hose end. A re-useable, typically aluminum fitting that accepts a rubber core, black nylon braided or stainless steel braided AN hose. It’s made up of a socket, and the fitting itself. The end of the hose is cut, the socket is installed onto the hose and socket with hose is installed onto the hose end. When someone says “AN Hose Ends” or “AN Hose Fittings” this is what they’re talking about. Fragola calls this a “Pro-Flow” hose end. Aeroquip simply calls it a “Reuseable Hose End”. Russell calls this a “Full Flow Swivel Hose End”, etc. They’re also available in low profile 45 degree and 90 degree versions. Fragola has two versions of this fitting, their series 2000 and series 3000. We only stock the series 2000 fittings, we can special order you the 3000’s if you must have them. The 2000 Series compression style Hose Ends use a nipple that the socket draws the hose over during assembly. These Hose Ends utilize the crush between the inside of the socket and the outside of the nipple to create it’s sealing area. The 3000 Series Cutter Style Hose Ends also use a socket to draw the hose over a nipple. But assembly directs the center portion of the hose into a cutter. The seal here is formed by the cutter embedding itself into the hose. We also have these in PTFE hose ends, they look nearly identical, but the application is much different.
  • Direct fit pro-flow hose ends: These are standard AN pro-flow hose ends with the adapters or connectors integrated.
    Direct Fit AN Hose Ends
  • Push lock barbed hose ends: This goes by several different names (Push-Lok, Push-Lite etc.) but the idea is the same. It’s a permanent, AN style barbed hose end. The connection is made by pushing the hose on the barb. We use Continental braided Conti-Tech hose with these fittings, found here. Clamps are optional but encouraged. Once the hose is pushed on, you typically have to cut the hose off to remove it. The hose is nearly half the price of standard AN hose but the fittings are roughly the same. They connect to any other AN adapters, or connectors the same as a standard AN fitting.
    Fragola AN Push Lock Barbed Hose End
  • PTFE Reusable hose ends: Fragola refers to these hose ends as “Real Street PTFE“, Russell calls them “PowerFlex”, other manufacturers have various names for them. They use a PTFE style hose (see below) and is most common in late model fuel system installs. While visually similar to a standard AN hose end, it uses a ferrule (also called an olive) under the stainless braiding, at the end of the PTFE inner liner. There are a couple extra steps involved during installation, but is the preferred hose and fitting combo in most cases.
    Fragola PTFE AN Hose End
  • Crimp on, Pro-Flow AN hose ends: Fragola refers to these as “Sport Crimp”. Sport Crimp is a standard AN Pro-Flow style hose end with a crimp on attachment instead of a nut. These are available in all common sizes and bends, all sizes except for -4an are swiveling. We also offer a crimp style PTFE fitting, these are what we use for our pre-made hose assemblies. All size crimped PTFE are non-swiveling.
    Fragola Sport Crimp Pro-Flow AN Hose Ends
  • Banjo Hose Ends: Banjo hose ends are something we don’t currently offer, but will be in the near future, this article will be updated when we do. We do currently offer the smaller steel 3AN and 4AN banjo adapters in our brake line fittings and adapters section. Banjo hose ends install directly onto a hose, banjo adapters install with a banjo bolt, and a standard hose end connects to the adapter. Banjo adapters are used where space is tight, fluid travels through the center of the banjo bolt, out through it’s sides, into the banjo itself. The banjo can be installed in any orientation required.
    AN to Banjo Hose Ends and Adapters
    AN to Banjo Hose Ends and Adapters

AN sizes explained

Sizes start at -2 (“dash two”, not “minus two”) through -32 in steps, each step is the outside diameter of the tubing in 1/16″ increments. For example a

  • -2 equals 2/16″ which is 1/8″
  • -3 equals 3/16″ which is… You guessed it 3/16″
  • -4 equals 4/16″ which is 1/4″
  • -6 equals 6/16″ which is 3/8″
  • -8 equals 8/16″ which is 1/2″
  • -10 equals 10/16″ which is 5/8″
  • -12 equals 12/16″ which is 3/4″
  • -16 equals 16/16″ which is 1.00″
  • -20 equals 20/16″ which is 1.25″
  • -24 equals 24/16″ which is 1.50″
  • -28 equals 28/16″ which is 1.75″
  • -32 equals 32/16″ which is 2.00″

AN thread sizes

Applies to all AN straight threads including those with flares, or non flare threads that seal with o-rings and washers.

  • -3 | 3/8-24 UNJF Straight Thread
  • -4 | 7/16-20 UNJF Straight Thread
  • -6 | 9/16-18 UNJF Straight Thread
  • -8 | 3/4-16 UNJF Straight Thread
  • -10 | 7/8-14 UNJF Straight Thread
  • -12 | 1 1/16-12 UNJF Straight Thread
  • -16 | 1 5/16-12 UNJF Straight Thread
  • -20 | 1 5/8-12 UNJF Straight Thread

AN metal tube O.D.

  • -3 | 3/16″
  • -4 | 1/4″
  • -6 | 3/8″
  • -8 | 1/2″
  • -10 | 5/8″
  • -12 | 3/4″
  • -16 | 1.00″
  • -20 | 1.25″

NPT Pipe thread sizing

  • 1/8″ NPT | 1/8-27
  • 1/4″ NPT | 1/4-18
  • 3/8″ NPT | 3/8-18
  • 1/2″ NPT | 1/2-14
  • 3/4″ NPT | 3/4-14
  • 1.00″ NPT | 1.00-11.5
  • 1.25″ NPT | 1.25-11.5

AN Fitting Torque Specs

A lot of people over tighten the aluminum hose ends on the adapters, distorting the flared seat that the fitting uses to seal, causing a leak. To avoid this, here’s the recommended torque specs. You can torque these with a torque wrench and an open end crows foot pictured below. Cheap crows foot wrench sets can be found on Amazon.

Open Ended Crows Foot on Small Torque Wrench
Open Ended Crows Foot on Small Torque Wrench

We tighten the fitting initially with an aluminum AN wrench to avoid scratching and torque the final amount with the torque wrench.

  • -3 = 9 ft/lbs
  • -4 = 12 ft/lbs
  • -6 = 17 ft/lbs
  • -8 = 29 ft/lbs
  • -10 = 35 ft/lbs
  • -12 = 45 ft/lbs
  • -16 = 70 ft/lbs
  • -20 = 85 ft/lbs