1/8" NPT Thread Specifications
Complete dimensions for 1/8" NPT (National Pipe Taper) thread per ASME B1.20.1. TPI: 27, Pitch: 0.03704" (0.941 mm). Taper: 1 in 16 on diameter (3/4" per foot).
Thread Dimensions
| Designation | 1/8" NPT |
| Nominal Pipe Size | 1/8" |
| TPI | 27 |
| Pitch | 0.03704" (0.941 mm) |
| Outside Diameter | 0.4050" (10.29 mm) |
| Pitch Diameter at E0 (hand-tight) | 0.36351" (9.233 mm) |
| Pitch Diameter at E1 (wrench makeup) | 0.37360" (9.489 mm) |
| Minor Diameter at E0 | 0.34560" (8.778 mm) |
| Taper Angle | 1.7899° (1:16 taper ratio, 3/4"/ft) |
| Thread Depth (h = 0.8p) | 0.02963" (0.753 mm) |
Values per ASME B1.20.1 Table 1. E0 = hand-tight engagement pitch diameter; E1 = wrench-makeup pitch diameter.
Tap Drill Size
Tap drill: R (0.3390" / 8.61 mm)
NPT tap drills allow the tap to cut the taper thread. The tap itself creates the taper geometry; drill size provides initial clearance at the large end.
Common Applications
- Plumbing connections
- Gas piping
- Hydraulic fittings
- Pneumatic connections