Complete Guide to Hoses & Fittings: Types, Functions, and How to Choose

When modifying or repairing a vehicle, hoses (lines) and fittings are essential components you simply can't overlook. Whether you're working on the fuel system, cooling system, or vacuum lines, choosing the right type of hose and matching fittings directly affects your build’s sealing performance, safety, and long-term durability.

This guide will walk you through the different types of hoses and fittings, explaining their key differences, functions, and best-use scenarios—perfect for both DIY enthusiasts and professional mechanics.

What Are Hoses and Fittings?

When working on a car—especially when upgrading or replacing fuel systems, cooling setups, or oil routing—you'll often hear about hoses and fittings. But what exactly are they, and why are they so important?

Basic Overview of Hose & Line Systems

A hose (or fuel line) is a flexible tube that carries fluid—like fuel, coolant, or oil—from one part of your vehicle to another. Think of it as the 'veins' of your car. Just like blood needs to move through your body, fuel and other fluids need to move through your car safely and efficiently.

Hoses come in different materials depending on what they’re carrying:

• Some are built for high temperatures (like those near the engine)
• Others are made for high pressure (like in fuel-injection systems)
• Some are resistant to chemicals like ethanol or diesel

Common Types of Fuel Lines & Hoses

Choosing the right fuel line is essential to building a reliable and safe fuel system. Whether you’re upgrading a street car, tuning a race build, or outfitting a marine engine, each type of fuel hose is made for a specific use case.

Here, we break down each fuel hose type in detail—so whether you’re building a high-performance street car or a marine engine, you’ll know what to use and why.

PTFE Fuel Lines

Features, Materials, and Use Cases (High temp, ethanol-safe)

PTFE (Polytetrafluoroethylene) fuel lines are the top choice for high-performance and high-temperature fuel systems. Known for their superior chemical resistance and ability to handle modern fuels like E85, methanol, and diesel, PTFE lines are durable, non-permeable, and long-lasting.

Material Composition:

• Inner layer: PTFE (polytetrafluoroethylene)
• Middle layer: Stainless steel core
• Outer layer: Stainless steel braid (silver finish), optionally with an outer black nylon sleeve for abrasion resistance

• Must use PTFE-specific fittings only

• Transmission fluid, coolant, oils, pump gases, racing gases, vacuum, hydraulic oil, diesel, regular fuel, and E85 gasoline

• High-performance, turbocharged, fuel-injected engines, E85 conversions

• High temperature rating (up to 500°F / 260°C)
• Rigid hose; avoid sharp bends or folds
• Provides superior chemical resistance and long-term durability

Running E85 on a turbocharged LS swap? A PTFE fuel line with stainless steel or nylon braided outer layer will ensure long-term performance without fuel seepage or vapor loss.

• Compatible Fittings: Designed to work with swivel (rotary) fittings and push-in fittings only.
• Compatible Fluids: Suitable for transmission fluid, coolant, oils, pump gases, racing gases, vacuum, hydraulic oil, diesel, and regular fuel.
• Limitations: Best not used with E85 gasoline, as it can reduce the hose’s lifespan.

Swapping in a fuel-injection system on your classic Mustang? A CPE braided fuel hose is a solid choice—easy to work with and built to last.

NBR Fuel Hoses

Budget-friendly option for low-pressure systems

NBR (Nitrile Butadiene Rubber) hoses are ideal for low-pressure fuel systems, especially older carbureted engines and small power equipment. While affordable and easy to install, they are not designed for ethanol-rich fuels or modern high-pressure setups.

• Compatible with: Gasoline (non-ethanol), diesel
• Best for: Lawn mowers, older carbureted cars, garden equipment
• Compatible Fittings: Only compatible with inverted flare fittings.

Note: Avoid using NBR hoses with E10, E85, or ethanol blends—they’ll degrade quickly.

Need an economical solution? Browse our NBR fuel hose collection for reliable low-pressure options.

Tip: CPE Fuel Lines VS NBR Fuel Hoses

Marine Fuel Hoses

Corrosion-resistant, ideal for marine or salt-heavy environments

Marine fuel hoses are engineered for saltwater exposure, UV resistance, and low permeation. These hoses meet EPA or USCG standards, making them a safe, compliant choice for all types of marine fuel systems.

Types of Fittings and How They Work

1. AN Fittings (Army-Navy Standard)

• Size System: Expressed as AN followed by a number (e.g., AN6, AN8), where each size corresponds to a specific hose inner diameter.
• Angles Available: 0°, 45°, 90°, 180°
• Threads: UNF (Unified National Fine) thread pattern
• Application: Used for fuel, oil, coolant, and other fluid systems
• Example: AN6 for fuel lines, AN10/AN12 for oil cooler setups.

Type of AN Fittings

• No clamps or collars needed
• Quick install
• Not ideal for high-pressure or PTFE lines

4. Swivel Fittings

• Prevents: Hose twisting during installation
• Best for: Tight or angled spaces
• Common Use: With CPE braided hoses

Swivel Fitting Installation Overview

1. Cut the hose cleanly and remove any tape at the end.
2. Insert the hose into the socket using a twist-push motion until fully seated.
3. Apply a small amount of oil on the fitting to ease assembly.
4. Screw the fitting into the socket until there’s a 1mm gap between the fitting and the socket.
5. Check that the socket hasn’t moved.

AN Swivel Fittings Size Reference Chart

5. Quick Disconnect EFI Fittings

• Tool-Free Install/Removal
• Best for: Modern fuel injection setups
• Note: Must match the vehicle’s fuel rail or filter end design

6. Y Block Fittings

7. Hardline, Barb, Weld-On, Cap & Plug Fittings

Includes hardline fittings, barbed, weld-on, and caps/plugs for custom fuel systems.

• Barbed Fittings: Often used with rubber or NBR hoses (requires hose clamps)

• Weld-On: Used in custom fuel tanks or aluminum lines

• Caps & Plugs: Sealed unused ports

Understanding AN Fitting Sizes

Thread compatibility:

• AN fittings use UNF (Unified National Fine) threads
• PTFE fittings typically require flare-style threads
• Barbed fittings use hose clamp retention (no thread sealant)

Pre-Made Fuel Line Kits vs. Custom Assemblies

Pre-Made Kits:

• Convenient, matched components
• Ideal for first-time installs or common applications (LS swaps, fuel filter lines)
• Usually includes fittings + hoses cut to length

Custom Assemblies:

• Allows precise routing and fit
• Useful for complex builds or tight engine bays
• Choose specific hose type, fitting angles (0°, 45°, 90°), and thread types

Tip: Always measure routing before cutting custom hose lengths. Add extra slack for movement/vibration.

Installation Tips and Best Practices

Sealing:

• Never use Teflon tape on AN or flare fittings
• Use PTFE paste or thread sealant for NPT threads only
• Ensure PTFE ferrules are seated correctly during assembly

Tools:

• Use aluminum AN wrenches to prevent scarring fittings
• Use soft-jaw vise blocks to protect fittings during tightening
• Rotary cutters or shears for clean hose cuts

Alignment:

• Mark hose/fitting alignment before tightening to detect twist
• Check socket or nut movement post-install
• Allow ~1mm gap between nut and fitting body (swivel types)

Warning: Cross-threading or improper sealing can lead to leaks or dangerous pressure failures.

FAQs

PTFE vs. CPE — What's the Difference?

• PTFE (Polytetrafluoroethylene) hoses feature a hard, non-stick inner liner that offers superior chemical resistance, higher temperature tolerance, and compatibility with aggressive fuels including E85, methanol, and brake fluids. They are ideal for high-performance or racing applications.
• CPE (Chlorinated Polyethylene) hoses have a rubber-like inner layer. They offer good flexibility and are compatible with most oils, fuels, and coolants, but not recommended for use with E85, as it may reduce lifespan.

In short, PTFE is more durable and chemically resistant, while CPE is more flexible and cost-effective.

Are Push Lock Fittings Reliable?

• Yes, Push Lock fittings are reliable for low- to medium-pressure systems (typically under 250 PSI).
• They don’t require hose clamps, making them quick to install. However, they’re not recommended for high-pressure fuel injection systems or under-hood areas with extreme heat.

For critical systems (like fuel delivery), consider using barbed fittings with clamps or AN fittings instead.

When Should I Use Quick Disconnects?

• Quick Disconnect (QD) fittings are ideal for EFI (Electronic Fuel Injection) systems, or any setup where you need to frequently remove or service lines.
• They allow tool-free connection/disconnection, reduce service time, and improve safety by minimizing fuel spillage.

Use QD fittings when ease of maintenance and fast swaps are top priorities.

Can You Mix Hose Types in the Same System?

• Technically, you can mix hose types (e.g., PTFE, CPE, rubber), but you must:
  • Match each hose with the correct fitting type
  • Ensure chemical compatibility (e.g., don’t use CPE for E85)
  • Check temperature and pressure ratings are consistent across the system

For best results and reliability, it’s recommended to standardize one hose type per system, especially for high-performance builds.

Recommended Products & Further Reading

Fuel Lines Collection

Explore a wide range of fuel hoses suited for various applications—PTFE, CPE, rubber, marine, and more.Browse the full collection: 👉 Fuel Line Kits & Hoses

Fittings Collection

Find the right fitting for your system: AN fittings, push lock, PTFE-specific, quick disconnects, and more.Browse the fittings collection: 👉 Hose Fittings & Adapters

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