1/8 NPT thread characteristics, identification, and application

1/8 NPT (National Pipe Taper) thread is a tapered pipe thread used mainly in hydraulic and pneumatic installations where a leak-tight connection without additional seals is required. The abbreviation NPT stands for "National Pipe Tapered," which indicates the characteristic tapering of the thread diameter towards the end of the fitting. Thanks to this, when tightened, the elements wedge together, creating a tight connection. The 1/8 NPT version has 28 threads per inch (TPI) and an outer diameter of approximately 9.7 mm, as confirmed by the pipe thread dimension table.

NPT tapered thread dimension table

Identification of 1/8 NPT thread

1/8 NPT thread can be recognized by:

• tapered shape – the diameter decreases towards the end,

• fine pitch – 28 threads per inch,

• outer diameter in the range of approximately 9.3–9.7 mm,

• characteristic shape of the thread crests at a 60° angle.
  To identify it, you can use a caliper and an inch thread gauge to confirm the tapered profile and the number of threads.

Application of 1/8 NPT thread

NPT threads are used where high pressure resistance and tightness are required without the need for additional seals. 1/8 NPT thread is used, among others, in:

• power hydraulics (pressure sensors, pressure gauges, test connections),

• pneumatics (connectors for compressed air hoses, actuators),

• fuel and oil installations,

• machine cooling and lubrication systems.

Why choose 1/8 NPT thread components at the Hydron store?

The Hydron store offers a wide selection of couplings, adapters, and plugs with 1/8 NPT threads made of high-quality steel or brass, ensuring durability and tightness of connections even in difficult industrial conditions. Thanks to extensive experience in power hydraulics and a certified ISO quality system, Hydron guarantees products that meet the requirements of professional users.

Technical parameters of 1/8 NPT thread:

• Thread type: NPT (tapered)

• Outer diameter: approx. 9.7 mm

• Pitch: 28 threads/inch

• Crest angle: 60°

• Standard: ANSI/ASME B1.20.1

Order 1/8 NPT thread components at the Hydron store and be sure of tight, durable connections in your hydraulic and pneumatic systems.

1/8 NPT thread dimensions in practice

Correct identification of 1/8 NPT thread dimensions is crucial when selecting system components. The "1/8" designation does not directly refer to the diameter measured with a caliper; therefore, measuring the outer diameter of the thread alone is not sufficient for its identification. 1/8 NPT thread has a specific number of threads per inch and a characteristic tapered shape that distinguishes it from threads BSP or metric. For this reason, it is recommended to use dimension tables and compare the pitch and thread profile angle for identification.

Differences between 1/8 NPT thread and other standards

One of the most common mistakes is confusing 1/8 NPT thread with a BSP thread of a similar diameter. Despite similar external dimensions, differences in the profile angle and sealing method mean that these threads are not compatible with each other. 1/8 NPT thread seals on the thread itself, while cylindrical BSP threads require sealing on the face of the connection. Attempting to connect these two standards can lead to leaks or damage to system components.

Other products and installation components

Components with 1/8 NPT threads are most commonly used in combination with measuring fittings and hydraulic connectors. In installation practice, this thread is found in pressure gauges, pressure sensors, as well as in thread adapters, which allow transitions between different thread standards. Complementing the installation are also thread sealants, such as tapes and pastes, which support the correct sealing of the tapered connection.

FAQ – frequently asked questions about 1/8 NPT thread

What are the dimensions of 1/8 NPT thread?

1/8 NPT thread has a specific outer diameter, a tapered shape, and a constant number of threads per inch. For its identification, it is best to use dimension tables and thread gauges.

Is 1/8 NPT thread a tapered thread?

Yes, NPT thread is a tapered thread and seals on the thread itself, without sealing on the face of the connection.

Can 1/8 NPT thread be connected with BSP?

No, NPT and BSP threads differ in profile angle and sealing method, so they are not compatible with each other.

How to seal 1/8 NPT thread?

PTFE tape or a sealing paste designed for tapered threads is used for sealing.

Where is 1/8 NPT thread most commonly found?

This thread is most commonly found in pressure gauges, sensors, valves, and hydraulic and pneumatic systems with smaller diameters.