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4Lifetimelimes Knowledge Garage



Bubble vs Double Flare Brake Lines

If you have never worked on your car brakes before, you’re wondering what a flare is. Internal parts of cars can seem super complex to owners of a vehicle. However, when you break it down into small parts it is much easier to piece it back together. When getting into brake lines the same things apply. One of the most important parts of a brake line is the flare. Flares need to be performed properly to keep a tight seal. If you notice leaking from your brake lines it is most likely from the quality or type of flare.


The Differences

When it comes to slowing down our cars, we do not put much thought into it. When we push down the brake pedal the force generated by your leg is amplified. Then a piston goes into the cylinder and pushes out the hydraulic fluid. After this action occurs, hydraulic fluid goes about the entire braking system's lines and hoses. The force is then equally split up to all four brakes and causes your car to stop by creating friction between the brake pads of your car. For all of this to work the way it is intended to, the seals need to be airtight. This is where the right flare comes into place.


Double Flare

The double flare is the most popular flare across the industry while being very common in Asian and American cars. The double flare may also go by SAE or Inverted. The double flare is able to fit many variations in the car makes and models.
The double flare goes inside a vehicle braking system twice. The double flare needs the single flare-shaped lip so that it can stay folded over the system. The single flare is very identical to the double flare. Although they look a lot alike, the double flare is much stronger and can hold more pressure built up inside the braking system. 


Bubble Flare

The double flare is a flare that is especially popular in vehicles imported from Europe. Just like the double flare, the bubble flare may also be called something else such as DIN or ISO. 
When creating a bubble flare, you have one less step. When someone is making a double flare, they actually start out by making a bubble flare before that. Some people mention that the bubble flare looks like the head on a screw. 



Image of a bubble flared brake line
Image of a double flared brake line

Tool Kit 

Our 4LifetimeLines Universal Hydraulic Flaring Tool is a tool that can flare any lines necessary for brake and fuel lines. This tool is a necessity for shops doing frequent brake and fuel line repairs. The tool splits into 4 main parts: The Yoke, Yoke Handle, Hydraulic Handle, and the Clamping Screw Rod. This kit is so simple and straightforward that any average DIY’er could handle it themselves.


4LifetimeLines' Hydraulic Flaring Tool LTFL-3


Can you use a bubble flare instead of a double flare?

The simple answer is no. The line and port are completely different and will not come close to sealing. When doing brake lines, you need to determine what type of flare you need for your car. One important thing to remember is to never use a single flare. Single flares are not durable enough to withhold the pressure and are to never be used on steel brake lines.


Quality of Flares 

Brake lines can leak after installment if they are not fitted properly. One of the most common problems is when the flare is imperfect. When the flare is not accurately done, it will cause a leak at the connection. When performing quality flares, it comes down to the tools you are using, the effort, and the attention to detail that goes into making the flare. 



The braking system of a car is arguably one of the most important components when it comes to driving down the road. By knowing the subtle differences between double and bubble-flared brake lines, you will save yourself from all of the stress and headaches. The differences between the two flares are quite small but are very important when it comes to fitting brake lines on your vehicle.

Did you enjoy reading our blog? If so, let us know by using promo code: BLOG10 at checkout and get 10% off of your order! 

Best of luck with your next project,

The 4LTL team

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  • Great info for a novice like me. Thanks, I’ve bought my brake lines and tools from you.

    Charles Cooke
  • Very useful, and informative, done most things on car,brake system all new to me,having to replace most of brake system in poor state on18yr old 3ser E46 bmw convertible!

    Anthony Peters
  • Best explanation I have ever read. A bubble compared to a double and which to use. Thumbs up!

  • simple, to the point, excellent writeup.

    mike gardner