How to find out what flare is on your brake line

How do I tell what kind of flare is on the end of my brake line?

There are two basic types of flares used on OEM automotive brake systems throughout the world. The SAE/double (inverted/45degree) flare and the DIN/ISO bubble flare. We will refer to them as SAE or DIN flare. The most common is the SAE flare. Typically found on all American and Asian cars, but the European style DIN flare is appearing everywhere now.

Never use a single flare on automotive components. The SAE/double flare standard is remarkably tolerant of production variations, but the assemblies must be the same standard. Single flares are never allowed on steel brake lines.

SAE/Double Flare

If your brake line looks like a tiny funnel going into the ID of the tubing, and the back side of the flare is at a 45 degree angle, then it is the SAE flare.

DIN/ISO Bubble Flare

If the end of the tubing looks like a button, and the back side angle of the flare is 90 degrees, than it is the DIN flare. You must use a nut with a "lead" for the DIN flare.

How do I tell what kind of flare I need if I don't have the brake lines? (Part 1)

Look in the port where the line goes. If the bottom looks like a volcano pointing up at you it is an SAE flare seat.

Pictured to the left is an SAE flare seat (45 degree inverted/double) on a UA1-3br union

How do I tell what kind of flare I need if I don't have the brake lines? (Part 2)

Look in the port where the line goes. If it looks funnel shaped going away from you it is a DIN flare seat.

Pictured to the left is a DIN flare seat (ISO/bubble) on a UM14-3 union

What if there is nothing in the bottom of the port?

On line locks, adjustable brake bias valves, etc. you sometimes will find no seat but a hole with a pipe thread in it. You will need an adaptor. You can adapt it to an SAE seat with our part number AD1br, but I recommend using our 37 degree adaptor, AN816-3. (Pictured on the left) We do not have DIN or metric SAE adaptors.

What is a 37 degree flare?

If you are fitting aftermarket/high performance parts you may run into 37 degree flares. The 37 degree flare was standardized as A.N. (Army/Navy) during WWII for aircraft use.AN/37 degree nuts and fittings accept single and double flares. It is acceptable practice to single flare Cunifer™ (seamless) brake line for use with AN/37 degree fittings. Never single flare steel brake line.