Understanding NPT vs NPTF Thread Connections for CNC-Turned Parts
In precision manufacturing, especially when producing CNC-turned parts like bulkhead fittings, understanding thread standards is critical. Two widely used thread types are NPT (National Pipe Taper) and NPTF (National Pipe Taper Fuel). While they look similar, the differences between them can affect sealing performance, compatibility, and overall reliability of fluid or mechanical systems.
In this article, we will answer common questions about these threads:
Is NPT compatible with NPTF?
How to tell the difference between NPT and NPTF?
What are NPTF fittings also called?
What is the standard thread for NPTF?
Understanding these points helps manufacturers, engineers, and buyers select the right thread type for their CNC-turned components.
What Are NPT and NPTF Threads?
NPT threads are tapered threads commonly used in plumbing, hydraulic systems, and industrial fittings. They form a seal when combined with a compatible female thread, usually with a thread sealant or tape.
NPTF threads are designed for a “dry seal” without the need for additional sealant. They achieve sealing through an interference fit, which allows fluid- or air-tight connections, particularly in high-pressure applications.
The main difference lies in the sealing method: NPT threads need sealant, while NPTF threads rely on precise interference for a leak-free connection.
Is NPT Compatible with NPTF?
Many people wonder if NPT and NPTF threads are interchangeable. The answer is cautiously yes:
NPT male threads can screw into NPTF female threads, and vice versa, because they share the same taper and pitch.
However, sealing performance may not be guaranteed when mixing types. NPTF’s dry seal design may not function as intended with an NPT thread without sealant.
For critical applications such as hydraulic systems or fuel lines, it is recommended to match NPT with NPT and NPTF with NPTF to ensure safety and reliability.
Selecting the correct thread type is essential for CNC-turned bulkhead fittings, valves, or connectors to prevent leaks and maintain long-term system performance.
How to Tell the Difference Between NPT and NPTF
Distinguishing between NPT and NPTF threads can be challenging because they appear similar. Here are some practical ways to identify them:
Look for the “dry seal” label – NPTF threads are often identified as dry seal or interference-fit threads.
Check thread geometry – NPTF threads are slightly modified to create a tight fit that seals without additional materials.
Thread pitch and taper – Both thread types share the same taper (1° 47′ or approximately 1.7899° per inch), which is why they can fit together, but NPTF may feel tighter when engaged.
Compare minor diameters – NPTF threads are designed with a minor diameter slightly larger than that of NPT, allowing the interference fit to seal.
Using thread gauges or technical charts is the most reliable way to confirm the type, especially for precision CNC-turned parts.
What Are NPTF Fittings Also Called?
NPTF threads are commonly referred to by several names:
Dry Seal Threads – emphasizing that they do not require sealant.
Fuel Threads – used in applications involving fuels, hydraulics, and high-pressure systems.
Interference Fit Threads – highlighting their sealing principle.
These terms may appear in product specifications or technical drawings. When sourcing or manufacturing CNC-turned parts, always confirm the thread type to avoid mismatched connections.
What Is the Standard Thread for NPTF?
NPTF threads are standardized under ASME B1.20.3, which defines:
Thread angle: 60°
Taper: 1° 47’ (1.7899° per inch)
Fit class: Interference fit for dry seal
Nominal sizes and tolerances: Ensures consistency and interchangeability
Following this standard ensures that CNC-turned parts, such as bulkhead fittings or hydraulic connectors, are reliable, leak-free, and compatible across different manufacturers and applications.
Why Understanding NPT vs NPTF Matters in CNC Turning
For manufacturers producing bulkhead fittings, hydraulic components, or precision threaded parts, understanding thread types is critical:
Sealing requirements – High-pressure applications often require NPTF threads for a dry seal.
Customer specifications – Clients may request NPT or NPTF based on their system needs.
Material considerations – Stainless steel, brass, or aluminum behave differently under torque; correct thread selection ensures proper sealing and durability.
Production consistency – Matching threads reduces leaks, customer complaints, and costly returns.
By understanding the differences, CNC turning shops can produce reliable parts that meet international standards.
Key Advantages of Using NPTF in CNC-Turned Parts
Leak-free performance without sealant – ideal for fuel, hydraulic, or pneumatic applications.
Consistent quality and tolerance – standardized threads ensure repeatable results.
Global compatibility – standardized ASME threads allow parts to work seamlessly in international systems.
Versatility – suitable for small and large CNC-turned components, including bulkhead fittings.
These advantages make NPTF a preferred choice for precision applications requiring high reliability and safety.
Conclusion
While NPT and NPTF threads may look similar, the differences in design and sealing mechanism are crucial for performance.
NPT threads require sealant, while NPTF threads provide a dry seal through interference fit.
Compatibility is limited; it is best to match thread types for critical applications.
NPTF threads are standardized under ASME B1.20.3 and are also known as dry seal or fuel threads.
For CNC turning manufacturers producing bulkhead fittings and precision threaded parts, understanding these standards ensures high-quality, leak-free, and globally compatible products. Selecting the correct thread type protects system integrity, reduces errors, and enhances customer satisfaction.