All about fittings

Ordering replacement fittings in an air suspension system can be daunting, so here's a guide to help figure out what you need.

Thread sizes

The most common thread size for air suspension is NPT (National Pipe Tapered), or sometimes BSP (British Standard Pipe).  The nomenclature can be confusing because the thread name does not correspond to the size of the thread. 

NPT Thread Chart with Metric Dimensions

Note that these threads are tapered, this means that the diameter gets gradually smaller toward the end.

Other thread sizes

BSP threads are very similar in size to NPT, the two are almost identical in size however they thread pitch (or TPI) is usually different and the two shouldn't be mixed up.

Metric pipe threads do exist, and these are generally a lot easier to measure in that the major thread diameter does actually correspond to the thread's name, so an M10 thread has a 10mm major diameter.

Air line sizes

With plastic air lines, the size generally refers to the outside diameter, and can be imperial or metric.  Occasionally with rubber air hoses or other hoses where the fittings are crimped on, these are quoted based on the internal diameter, but for the most part we use push fit connectors so those don't really apply here.

Imperial to Metric air line conversion

Note: Metric air lines should never be used with imperial fittings!

Fitting types

Modern systems all use push fit (or PTC - push to connect) air line fittings.  These are far more convenient than the old compression style fittings. 

Compression fittings are available though, and these are necessary for use with stainless steel hard lines.

Barbed fittings are also available, these are preferable when using the low pressure flexi air lines.  They can be used with nylon air line as well though, and while they are hard to use they are useful for tight installations where the air line could flex a little bit near the fitting. 

Push fit connectors work perfectly with plastic air lines, and they also work just fine with softer metal lines such as copper and aluminium.

Air line types

There are many types of air line.  Nylon and Polyurethane are the most common due to their ease of use. It is crucial when buying air line for air suspension to ensure that they comply with regulations.  The most common type is J844, often referred to as DOT approved, there are cheaper, non approved versions around, so take care when ordering.  All of the nylon air lines we sell meet these standards.

Copper and aluminium are preferable when they are on show, however we generally advise running nylon air lines where possible.  Stainless steel air line is available as well, this is great for longevity because the air lines are very hard and don't lose their shine, however stainless steel can't be used with push fit connectors.

Braided leader lines are useful although not strictly required, when running air lines from the chassis to moving suspension components.

Finally, when cutting air lines, it's very important to use a proper cutter to get a perfectly straight and burr free cut.