NPTpipe60° flankASME B1.20.1

4-8 NPT taper Thread Dimensions

4-8 NPT is a pipe National Pipe Taper thread. There are 8 threads per inch on a 4.5 in major diameter, giving a metric-equivalent pitch of 3.175 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 Ø4.5 in

Threads per inch8

Pitch (metric)3.175 mm

Pitch Ø4.4189 in

Tap drill—

Thread profile

millimetres unless stated

4-8 NPT taper — basic profile60° flank angle · Not to scale

Basic information

Designation: 4-8 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: 4.5 in / 114.3 mm
Pitch (metric equivalent): 3.175 mm
Threads per inch: 8
Pitch diameter: 4.4189 in / 112.24 mm
Minor diameter (external): 4.3189 in / 109.7 mm
Minor diameter (internal): 4.3646 in / 110.86 mm
Thread depth: 0.1 in / 2.54 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 4-8 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.

2-11.5 NPT taper 2-1/2-8 NPT taper 3-8 NPT taper 3-1/2-8 NPT taper