NPTpipe60° flankASME B1.20.1

1/8-27 NPT taper Thread Dimensions

1/8-27 NPT is a pipe National Pipe Taper thread. There are 27 threads per inch on a 0.4051 in major diameter, giving a metric-equivalent pitch of 0.941 mm. The size label is a nominal bore rather than a diameter.

Note. Diameters are quoted at the gauge plane. The thread is tapered 1:16 on diameter, so the actual size changes along the thread.

Major Ø0.4051 in

Threads per inch27

Pitch (metric)0.941 mm

Pitch Ø0.3811 in

Tap drill—

Thread profile

millimetres unless stated

1/8-27 NPT taper — basic profile60° flank angle · Not to scale

Basic information

Designation: 1/8-27 NPT
Thread system: National Pipe Taper
Series: pipe
Standard: ASME B1.20.1
Basic profile: Unified profile, 0.8P thread height
Flank angle: 60°

Dimensions

Major diameter: 0.4051 in / 10.29 mm
Pitch (metric equivalent): 0.941 mm
Threads per inch: 27
Pitch diameter: 0.3811 in / 9.68 mm
Minor diameter (external): 0.3512 in / 8.92 mm
Minor diameter (internal): 0.365 in / 9.27 mm
Thread depth: 0.0296 in / 0.753 mm
Recommended tap drill: Not applicable — see note

How these values are derived

tabulated standard values

This is a pipe thread, so the published dimensions are tabulated values from ASME B1.20.1 rather than figures derived from a formula: a pipe size is a nominal bore, and the relationship between that bore and the thread diameter is historical, not geometric. Diameters are quoted at the gauge plane; the thread itself is tapered, so the actual size changes along its length.

Compatible parts0 specification pages

No specification in this database uses 1/8-27 NPT taper. That is expected: the catalogue covers machine screws, bolts, nuts and washers, and pipe threads belong to fittings, which are a separate family of parts. The dimensions above are still the standard ones for the thread itself.

Neighbouring sizes in National Pipe Taper.

1/16-27 NPT taper 1/4-18 NPT taper 3/8-18 NPT taper 1/2-14 NPT taper 3/4-14 NPT taper