Hose & Fitting Guide
Building a fuel, oil, coolant or pressure line does not need to be complicated. Start with the application, choose a suitable hose, match it with the correct hose ends, then use adapters to connect the finished hose assembly to the vehicle.
Start With the Application
One of the easiest mistakes to make is starting with the fitting. Before deciding that you need a -6AN fitting, establish what the hose actually needs to do.
What Are You Carrying?
Fuel, ethanol fuel, engine oil, transmission fluid, coolant, brake fluid, refrigerant, air or vacuum all place different demands on the hose.
How Hard Is It Working?
A breather hose and a high-pressure fuel or power steering line may look similar but operate in very different environments.
How Hot Will It Get?
Consider both the fluid temperature and external heat from exhaust manifolds, turbochargers and engine bays.
Where Does It Need to Go?
Hose length, bend radius, fitting angle, movement, abrasion and available space all affect component choice.
Choosing the Right Hose
Hose construction determines what fluids, temperatures and pressures the hose can safely handle. Always confirm the specifications of the individual hose before use.
Rubber Braided Hose
100 Series hose typically uses a synthetic-rubber inner reinforced and protected by an outer braid.
It is commonly used for fuel, oil, coolant and other performance plumbing applications where the particular hose is suitably rated for the fluid, pressure and temperature involved.
Depending on the manufacturer, 100 Series hose may be designed for cutter-style or taper-style reusable hose ends. These fitting systems are similar in appearance but are not interchangeable.
PTFE Braided Hose
200 Series hose uses an inner PTFE liner surrounded by a protective and reinforcing braid.
PTFE has excellent chemical compatibility and very low vapour permeability, making appropriately rated PTFE hose particularly useful in modern fuel systems and installations where fuel odour is undesirable.
PTFE hose requires hose ends designed specifically for PTFE construction.
Push-Lock Hose
Push-lock hose is designed to push over a matching barbed hose end, producing a simple and compact assembly without the reusable socket used by many braided-hose systems.
It is useful for many fuel, oil, coolant and breather applications where its pressure, temperature and fluid ratings are suitable.
Terms such as 100 Series, 200 Series and 400 Series are widely used throughout the performance plumbing industry to describe common hose families, but the exact construction and specification can vary between manufacturers. Always check the specifications of the actual product being used.
Specialist Hose & Tube
A/C Hose
Air-conditioning hose is specifically designed for refrigerant systems and the associated operating pressures. Use only hose and fittings suitable for the refrigerant and system involved.
Nylon Tube
Compact nylon tube is useful for air, vacuum, sensors, gauges, boost control and other small-line installations where suitable for the application.
Vacuum Hose
Vacuum hose is designed to retain its shape when subjected to negative pressure. Unsuitable hose can collapse inward when exposed to vacuum.
Brake Hose
Flexible brake hose is a safety-critical component. Road-going brake hoses and assemblies must comply with the applicable legal and engineering requirements for the vehicle.
Hard Line
Steel, stainless-steel and aluminium tube can provide a compact and tidy solution for suitable fuel, oil, coolant and other fluid systems.
Understanding AN Sizes
Dash sizes such as -4, -6, -8 and -10 are used throughout motorsport plumbing. The number is based on sixteenths of an inch.
| AN Size | Fraction | Nominal Reference |
|---|---|---|
| -3AN | 3/16" | 4.8 mm |
| -4AN | 4/16" / 1/4" | 6.4 mm |
| -6AN | 6/16" / 3/8" | 9.5 mm |
| -8AN | 8/16" / 1/2" | 12.7 mm |
| -10AN | 10/16" / 5/8" | 15.9 mm |
| -12AN | 12/16" / 3/4" | 19.1 mm |
| -16AN | 16/16" / 1" | 25.4 mm |
The dash-size system provides a nominal sizing reference. Actual hose inside diameter and outside diameter vary with hose construction and manufacturer. A -6 rubber braided hose and a -6 PTFE hose therefore do not necessarily have identical physical dimensions.
Match hose ends using the specified hose family and AN size, rather than measuring the hose and assuming its size.
AN sizing originated from a military specification intended to provide standardised connection sizes. In theory, fittings built to the same interface standard should be dimensionally compatible.
In practice, manufacturers work within their own production tolerances and design their hose and hose ends as a matched system. Hose wall thickness, outside diameter, nipple geometry, socket dimensions and assembly method can vary between brands.
For this reason, mixing hose and hose ends from different manufacturers is generally not recommended, even where the nominal AN size is the same. Wherever possible, use hose and hose ends specified by the manufacturer as a compatible system.
Match the Hose End to the Hose
The AN size alone does not determine compatibility. Hose ends must also be designed for the construction of the hose being used.
A -6 PTFE hose, -6 rubber braided hose and -6 push-lock hose can all be described as -6, while requiring completely different hose ends.
Even within conventional braided-hose systems, cutter and taper hose ends are different designs. Match the hose, hose-end family and manufacturer wherever possible.
Cutter & Taper Hose Ends
Conventional braided rubber hose commonly uses reusable cutter-style or taper-style hose ends. Both systems use a socket and nipple arrangement to capture the hose, but their internal geometry and sealing method differ.
Use the fitting system specified for the particular hose rather than assuming that cutter and taper fittings of the same AN size are interchangeable.
PTFE Hose Ends
PTFE hose ends commonly use an olive or ferrule to capture and seal the PTFE liner. They must be matched to the correct PTFE hose.
Push-Lock Ends
Push-lock fittings use a pronounced barb designed to retain compatible hose. Follow the hose and fitting manufacturer's requirements regarding clamps and assembly.
A/C Hose Ends
Designed specifically for refrigerant hose systems and normally installed using the appropriate crimping method and equipment.
Brake Hose Ends
Brake-hose fittings are designed for the specialised hose, pressure and sealing requirements of braking systems. Compliance requirements also apply to road-going vehicles.
Tube Fittings
Tube nuts, sleeves, olives and other fittings allow rigid tube to connect to components or transition into flexible plumbing.
How the Whole Assembly Fits Together
It helps to separate the hose assembly from the adapter used to connect it to the vehicle.
or Port
Connection
Hose
Carries the fluid between components.
Hose End
Mechanically attaches to the hose and provides the connection at the end of the hose assembly.
Adapter
Converts the hose assembly's connection into the thread, port or connection used by the component.
AN, ORB, NPT, BSP & Metric
Identifying the thread is only part of identifying a fitting. You also need to know how the connection is designed to seal.
AN / JIC
AN-style flare fittings use mating 37-degree flare surfaces to create the seal. The straight thread pulls the two flare faces together but is not itself the primary sealing surface.
ORB
O-Ring Boss fittings use a straight thread with an O-ring sealing against a machined section of the port. The thread retains the fitting while the O-ring provides the seal.
NPT
NPT uses a tapered pipe thread. The male and female threads tighten progressively as they engage and form part of the sealing arrangement.
NPT sizes are nominal pipe sizes and should not be compared directly with AN dash sizes. A fitting described as 1/4" NPT does not have a 1/4" diameter thread.
BSP
BSP fittings may use parallel or tapered threads and can employ different sealing methods. Similar-looking pipe threads are not automatically interchangeable.
Metric
Metric describes the thread form and size rather than a single sealing method. Automotive metric fittings can use flare seats, O-rings, sealing washers and other arrangements.
Two connections can appear to have similar or even matching threads while using completely different sealing methods. Always identify both the thread and the sealing surface.
The 37-degree flare surfaces create the seal in a standard AN flare connection. Thread-sealing tape is therefore not used on the AN flare thread itself.
Pipe-thread sizing can be particularly confusing. Sizes such as 1/8", 1/4", 3/8" and 1/2" NPT are nominal pipe sizes, not measurements of the thread outside diameter.
Do not assume, for example, that 1/4" NPT is physically equivalent to -4AN because both contain the number four or refer to a quarter inch. They are entirely different sizing systems.
Adapters, Unions, Bulkheads & More
Once you have a hose assembly, adapters allow it to connect neatly to pumps, rails, regulators, tanks, coolers, engines, transmissions and other components.
Adapters
Convert between connection types, for example NPT to AN, metric to AN or ORB to AN.
Reducers & Expanders
Transition between two different fitting sizes where required by the installation.
Unions
Join two compatible hose ends or fittings together, often using a male connection at each side.
Bulkhead Fittings
Provide a secure connection through a panel, firewall, tank wall or bracket rather than passing flexible hose through an exposed hole.
Banjo Fittings
Allow a compact fluid connection where space around the port is restricted, such as turbochargers, brakes and other tightly packaged components.
EFI Quick Connects
Connect performance plumbing to common OEM-style fuel rails, pumps, filters and flex-fuel sensors using their original quick-connect interfaces.
Tees & Y-Pieces
Split or combine plumbing paths for sensors, fuel circuits, breather systems and other installations.
Plugs & Caps
Seal unused male or female ports during installation, servicing or system changes.
Sensor Adapters
Add pressure, temperature and other sensors to a fluid system while retaining suitable plumbing connections.
Straight, 45°, 90° or 180°?
Fitting angle and hose bend radius need to be considered together. The goal is to give the hose a natural path without kinking, twisting or placing unnecessary load on the hose end. This becomes increasingly important with larger PTFE hose.
Straight
Best where the hose has enough room to leave the component naturally before changing direction.
45 Degree
Useful where the hose needs an immediate but relatively gentle change in direction.
90 Degree
Helps route hose cleanly away from a component where a straight fitting would require an excessively tight hose bend.
180 Degree
Common around fuel rails, tanks and other installations where the hose needs to reverse direction in a compact space.
Avoid selecting an angled fitting simply because it looks neater. The goal is to minimise strain, tight bends, twisting and contact with hot, sharp or moving components.
Minimum bend radius is especially important with PTFE-lined hose. PTFE should not be forced into a tighter curve simply because the outer braid appears capable of making the bend.
As hose size increases, the required minimum bend radius generally increases substantially. Larger PTFE hoses can therefore require much more installation space than expected.
Bending a hose tighter than its specified minimum radius can kink or deform the liner, restrict flow and shorten hose life. Always check the minimum bend radius published for the exact hose being used.
Measuring an Existing Fitting
Do not identify a fitting from one measurement alone. Thread diameter, pitch and sealing surface all matter.
Flow passage size, hose inside diameter and AN dash size are not the same measurement. Use the thread and fitting specifications to identify an AN connection.
Building a Hose
Assembly technique varies between hose families and fitting manufacturers, but every successful installation starts with compatible components and clean workmanship.
Before Assembly
- Confirm hose and hose-end compatibility.
- Confirm fluid, pressure and temperature ratings.
- Plan routing before cutting hose.
- Allow for fitting length and hose engagement.
- Use suitable cutting and assembly tools.
Before Installation
- Inspect every assembled fitting.
- Remove cutting and assembly debris.
- Clean the inside of the finished hose.
- Check routing and clearance.
- Leak or pressure test where appropriate.
Braking, air-conditioning, high-pressure hydraulic and other safety-critical systems may require specialised components, equipment, testing or licensed work. Use components and procedures appropriate to the particular system.
Common Plumbing Mistakes
Wrong Hose-End Family
Matching AN size does not make a PTFE hose end compatible with conventional braided hose, or vice versa.
Confusing AN Size With Hose Bore
Dash size is a nominal system and does not guarantee a particular actual hose inside diameter.
Ignoring the Sealing Surface
Threads hold fittings together. Depending on the system, the seal may occur at a flare, O-ring, washer or tapered thread.
Using the Wrong Hose for the Fluid
Appearance does not establish chemical compatibility. Check the hose specification for the fluid being used.
Forcing Tight Bends
Choose fitting angles and hose routing that respect the hose's bend radius and minimise mechanical strain.
Skipping Final Cleaning
Cutting and assembling hose can leave debris inside. Clean the completed assembly before connecting it to a fuel, oil or hydraulic system.
Ready to Build Your Hose?
Choose your hose type and size, select the ends you need, then enter your finished hose lengths. The OZ Motorsport Hose Builder will show compatible components and help work out an efficient combination from the available hose lengths.
Open Hose Builder
