How To Choose And Use Hardline

By: Jeremy Stoermer11/02/2018 < Back to Blog Home

With all the choices and differences in tubing materials today, choosing the correct hardline can seem daunting. Each material has its own pros and cons so you’ll need to consider the specific application or vehicle system that you plan to use it on, before making a purchase. Earl’s carries a wide selection of tubing in a variety of materials and sizes for use in most any automotive system. Follow along while I break down these tubing designs and give you a better idea of their benefits.

Steel hardline is one of the most common types of tubing, it’s used in most every system found in the automotive world, and for a good reason. To start off, it’s typically the least expensive to purchase and is fairly easy to bend, cut, and flare with common hand tools. Earl’s offers 2 types of steel hardline. Our Zinc plated steel tubing uses a double wall low carbon steel that is copper brazed and then zinc plated to resist corrosion. The other option is our Olive Steel hardline. It also is constructed of copper brazed double wall low carbon steel, but it’s also wrapped in a PVF or (poly-vinyl-fluorine) coating. The olive colored PVF coating provides superior corrosion protection and is ideal for vehicles exposed to snow, salt, gravel or any other harsh environment. Both designs are easy to bend, cut, and flare. For your convenience, Earl’s offers a large selection of tools to do everything from cutting, bending and flaring your hardlines. 

Aluminum tubing, is another popular choice that you’ll see. One of the greatest pros to using aluminum is that it’s easy to bend! So easy that you can bend it by hand, but it can also be difficult to get it perfectly straight, especially when purchased in rolls. Aluminum is easy to cut and flare and you can even polish it to a high sheen. Typically only the 37deg single flare method is used with aluminum since it’s such a soft material and is difficult to get quality flares when attempting 45 deg double flares. . Aluminum tubing can be used for everything from fuel, transmission, and oil supply lines, even vacuum and coolant lines. But aluminum tubing should never be used for pressurized brake lines. It’s common to see aluminum fuel and transmission lines and Earl’s EZ-Beader tubing tool allows you to connect a rubber hose directly to your aluminum tubing. The tool creates a radiused bead at the end of the tubing which can be used to retain the hose along with a hose clamp. Use EZ-Beader Tool part number 008ERL for 3/8” tubing & 009ERL for ½” tubing.


To get the best of both worlds Earl’s offers Easy-Form tubing. It’s tubing made from a copper-nickel alloy that is just as strong as steel, but much easier to cut, bend, and flare much like aluminum. Not be confused with the typical copper tubing you’ll find at the hardware store, Earls Easy-form tubing is composed of approximately 90% copper and 10% nickel. This tubing is so easy to bend you can do it with your bare hands but using a specialized bender can give you a perfect radius everytime . Companies like Volvo®, Audi®, and Porsche® have been using this type of copper-nickel alloy brake tubing since the 1970's. One of the biggest benefits of Easy-bend tubing is that it doesn't rust or corrode and is DOT approved for use on hydraulic brake systems. It’s ideal for use on all automotive hardline systems including brake lines, transmission cooler lines, fuel lines, etc. Earl’s offers Easy-form tubing in most popular diameters.

Stainless steel tubing despite its higher initial cost, still remains a popular choice among automotive enthusiasts. Despite being slightly more difficult to bend, stainless can be a great choice whether you’re looking for superior rust and corrosion resistance or need a tubing that can be polished to a show car shine that will last for years. Stainless tubing performs well with single flares and can be double flared but will require a high quality flaring tool like Earl’s P# 001erl to perform the operation correctly.

When it comes to flaring any tubing there are a few do and don’ts that you’ll need to know. The automotive standard is the 45 deg double flare. Double flaring folds the smooth outer portion of the tubing inward to form the sealing surface. This smooth surface combined with the extra material as a result of the doubled wall thickness, will give you a more reliable seal that is also less prone to cracking. The double flare method does not require the use of tube sleeves and is a good technique to use when working with mild steel and Easy-form tubing. Aluminum tubing is very soft and malleable making it difficult to perform quality double flares.

The 37 deg single flare can also be used on all 3 of the mentioned tubing types but requires that you use tubing sleeves and tube nuts to ensure a quality seal. You should always double check the flared area for cracks or weak spots before final installation.    

Stainless steel is a considerably harder material, and a single 37 degree flare is usually sufficient. When using the single flare method you’ll have to use tube sleeves and tube nuts to securely seat the flare to the fitting. Earl’s carries a variety of steel and aluminum tube sleeves and nuts for use with 37 deg AN fittings. 

You should never interchange 37 deg and 45 deg fittings, the difference in seat angles results in a very narrow sealing surface and can fail under pressure.

Now if you simply don’t want to mess with flares and flaring tools, Earl’s has an alternative for you. It’s our complete line of compression fittings which are designed to adapt hardline tubing to AN style fittings. They make it possible to easily adapt hardline tubing ranging from ¼” to ½” in diameter to an AN style fitting. Earl’s compression fittings are rated to 250 PSI and should never be used on a brake system.

When you’ve finished the assembly, don’t forget to use our handy pressure test kit P# D016-SERL to pressure check your work before final installation. It can save you time and money by preventing the loss of expensive fluids.

Securely mount your hardlines with our Adel clamps (part numbers 1710xxERL), or Line Clamps (part numbers 1702xxERL). They help prevent vibration and excessive flex in the lines which can cause cracks or even premature failure.

Just as Sir Francis Bacon said “knowledge is power”.  And I hope that with this information and some help from Earl’s you’ll have a better understanding of hardline applications and compatibility.

For more information on these products and to view our complete line of hardline tubing and tubing accessories visit our website at Earl’