3/8-18 NPS Thread Dimensions
3/8-18 NPS is a pipe National Pipe Straight thread. There are 18 threads per inch on a 0.6748 in major diameter, giving a metric-equivalent pitch of 1.411 mm. The size label is a nominal bore rather than a diameter.
Thread profile
millimetres unless statedBasic information
- Designation
- 3/8-18 NPS
- Thread system
- National Pipe Straight
- Series
- pipe
- Standard
- ASME B1.20.1
- Basic profile
- Unified profile, 0.8P thread height
- Flank angle
- 60°
Dimensions
- Major diameter
- 0.6748 in / 17.14 mm
- Pitch (metric equivalent)
- 1.411 mm
- Threads per inch
- 18
- Pitch diameter
- 0.639 in / 16.23 mm
- Minor diameter (external)
- 0.5945 in / 15.1 mm
- Minor diameter (internal)
- 0.615 in / 15.62 mm
- Thread depth
- 0.0444 in / 1.129 mm
- Recommended tap drill
- Ø 0.6193 in / 15.73 mm
How these values are derived
tabulated standard valuesThis 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 3/8-18 NPS. 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.
Related
Neighbouring sizes in National Pipe Straight.