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Inverted Flare Fittings


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Inverted flare fittings allow you to make the most out of your hydraulic brake lines, power steering lines, transmission cooler lines and fuel lines. An inverted flare makes it possible for you to get the most out of each line. In fact, this style of fitting is great for customers with performance and racing engines that experience a lot of vibration on their systems. The style makes them easy to replace if necessary, so you won’t have to worry about needing to buy a brand new line. Short nuts (available in brass or steel) are also available for an even more compact installation.

An inverted flare fitting, sometimes referred to as a double flare, forms a high pressure,  fluid tight seal. Inverted flare fittings use a 45 degree sealing surface. The seal takes place between the female side of the fitting or flare seat and the mating of that to the inside of the flare on the tubing.  A male tubing nut gets tightened against the flare and it then pushes the inside of the flare against the female flare seat as the nut engages and tightens in the female thread. Inverted flare male fittings are also available that stand alone and will screw into a female inverted flare fitting. These types of fittings will not use the traditional tubing nut and brake or fuel line tubing we are used to using. A good example of a stand alone fitting would be Speedway part # 9103186, inverted flare plug. It simply gets screwed into the female fitting, and it seals the seat off. 

A few of the common terms associated with inverted flare fittings are as follows:

  • IFF stands for Inverted flare female, which would be a fitting with a female cavity, internal threads and a flare seat.
  • IFM stands for Inverted flare male, which could be a flare nut, or a fitting that has the inverted flare machined on it and the male thread all in one.
  • Example: 3/8-24 IFF would stand for 3/8-24 thread pitch with an Inverted female thread, 3/8-24 IFM would it’s counterpart in male

Some of the most common thread sizes  of inverted flare fittings commonly used in automotive are 3/8-24, 7/16-24, ½-20, 9/16-18 and 5/8-18. We’ll speak in generalities here, but usually, 3/16  line will use a 3/8-24 flare nut, ¼”  line will use a 7/16-24 flare nut, 5/16” line a ½-20 flare nut and 3/8 line will use a 5/8-18 flare nut. Sometimes you’ll see large thread sizes on smaller line sizes, and this is common in some OEM braking systems, such as the large 9/16-18 fitting size on GM proportioning valves that were used with smaller 3/16 or 7/16 hard line. 

You can make your own inverted flare by buying a handy inverted flare, or double flaring tool in a 45 degree configuration. Normally, an inexpensive tool can do effective inverted flares on softer material, but if you are going to be double flaring a little harder material, a quality tool is a must. Speedway flaring tool 91170081 will do a wonderful job. DIY double flares on stainless steel tubing are not recommended due to the very hard nature of stainless steel. 

The handy inverted flare is used widely in hard brake lines and in braking systems. It is also used frequently in high pressure power steering systems in cars and trucks as well as fuel systems. Getting familiar with inverted flare fittings and learning to quality at home flares will be a feather in any car builder’s cap. 

Speedway Motors offers a huge supply of double flare tools and double flare fittings. We also offer a big variety of specialty, inverted flare adapter fittings that will take you from one size to another in one easy fitting. They can also adapt inverted flare to other styles of fittings such as AN style fittings or NPT (national pipe thread). We have tons of handy tubing kits that includes the brake line tubing, flare nuts and associated other inverted flare fittings necessary to plumb a typical braking system. An example of this would be #91095121.