Race Plumbing -- Compatibility and Adapters

When altering plumbing arrangements, it's important to understand what you may encounter that is already in place.


SAE fittings are common in many US made cars. They use the same threads as AN fittings, but use a different, incompatible flare system. Adapters should always be used when mixing SAE and AN fittings, despite the fact that the threads appear to fit.

The short version of the flare story is that AN fittings use 37 degree single flares, and SAE fittings use 45 degree double flares. If you crank them down really hard, they may seal, but not reliably. Just use the appropriate adapter and move on.


Metric ISO fittings are used on many non-US cars. Fittings are metric (M10x1.0 is common for brake lines, for example.) At least with these, you can't fool yourself into not using the adapters, it just won't work. Flares are a different type of double flare, which makes a diamond shape at the end of a line. These are often called bubble flares.

Pipe Thread

Pipe Thread is evil. Unfortunately, it's common and must be dealt with. More on this later.

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