When it comes to performance plumbing, choosing the right fittings is crucial. At anfittings.co.nz, we don’t just stock AN fittings – we also offer a wide range of metric fittings and NPT fittings to suit different applications. Understanding the difference between these thread types can save you a lot of time, money, and frustration when building or repairing your fuel, oil, or cooling system.
What Are Metric Fittings?
Metric fittings are designed using the metric measurement system (millimetres). These fittings are commonly used in European and Japanese vehicles, as well as in some aftermarket performance parts. Metric fittings are usually identified by their thread pitch and diameter, for example M12x1.5.
Key features of metric fittings:
Measured in millimetres (e.g. M12, M14, etc.)
Common in OEM (factory) automotive applications
Often used in engines, fuel rails, and cooling systems
Require precise thread matching to avoid leaks
If you’re working on a car that was built outside of the US, there’s a good chance you’ll come across metric threads at some stage.
What Are NPT Fittings?
NPT stands for National Pipe Taper, a thread standard widely used in the United States and in many performance applications. Unlike metric fittings, NPT threads are tapered, meaning the thread becomes tighter as it screws in. This creates a mechanical seal when combined with thread sealant or PTFE tape.
Key features of NPT fittings:
Measured in inches (e.g. 1/4” NPT, 3/8” NPT)
Common in aftermarket and performance parts
Tapered thread for sealing under pressure
Often used in fuel pumps, regulators, and sensors
NPT fittings are especially popular in high-performance builds where a strong, leak-free seal is essential.
Metric vs NPT – The Big Differences
While both types of fittings look similar, metric and NPT are not interchangeable. Here’s why:
Measurement system – Metric is in millimetres, NPT is in inches
Thread style – Metric is straight-threaded, NPT is tapered
Applications – Metric is common in OEM parts, NPT is common in aftermarket and performance parts
Trying to force the wrong fitting can damage components and cause leaks – so it’s always best to match the thread type to your system.
Choosing the Right Fitting
At anfittings.co.nz, we stock both metric fittings and NPT fittings, along with a huge range of AN hose ends, adapters, and accessories. Whether you’re building a custom fuel system, replacing factory parts, or upgrading for motorsport, we’ve got the fittings you need to get the job done right.
If you’re unsure whether your system requires metric, NPT, or AN fittings, feel free to reach out – we’re always happy to help point you in the right direction.
With the right fittings, you can achieve a leak-free, reliable setup that’s built to last.