8" NPT Thread Specifications
Complete dimensions for 8" NPT (National Pipe Taper) thread per ASME B1.20.1. TPI: 8, Pitch: 0.12500" (3.175 mm). Taper: 1 in 16 on diameter (3/4" per foot).
Thread Dimensions
| Designation | 8" NPT |
| Nominal Pipe Size | 8" |
| TPI | 8 |
| Pitch | 0.12500" (3.175 mm) |
| Outside Diameter | 8.6250" (219.07 mm) |
| Pitch Diameter at E0 (hand-tight) | 8.43359" (214.213 mm) |
| Pitch Diameter at E1 (wrench makeup) | 8.48359" (215.483 mm) |
| Minor Diameter at E0 | 8.33706" (211.761 mm) |
| Taper Angle | 1.7899° (1:16 taper ratio, 3/4"/ft) |
| Thread Depth (h = 0.8p) | 0.10000" (2.540 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: 8-5/16" (8.3125" / 211.14 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