4" NPT Thread Specifications
Complete dimensions for 4" 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 | 4" NPT |
| Nominal Pipe Size | 4" |
| TPI | 8 |
| Pitch | 0.12500" (3.175 mm) |
| Outside Diameter | 4.5000" (114.30 mm) |
| Pitch Diameter at E0 (hand-tight) | 4.33438" (110.093 mm) |
| Pitch Diameter at E1 (wrench makeup) | 4.38438" (111.363 mm) |
| Minor Diameter at E0 | 4.23785" (107.641 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: 4-1/4" (4.2500" / 107.95 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