1-1/4" NPT Thread Specifications
Complete dimensions for 1-1/4" NPT (National Pipe Taper) thread per ASME B1.20.1. TPI: 11.5, Pitch: 0.08696" (2.209 mm). Taper: 1 in 16 on diameter (3/4" per foot).
Thread Dimensions
| Designation | 1-1/4" NPT |
| Nominal Pipe Size | 1-1/4" |
| TPI | 11.5 |
| Pitch | 0.08696" (2.209 mm) |
| Outside Diameter | 1.6600" (42.16 mm) |
| Pitch Diameter at E0 (hand-tight) | 1.55713" (39.551 mm) |
| Pitch Diameter at E1 (wrench makeup) | 1.58338" (40.218 mm) |
| Minor Diameter at E0 | 1.51912" (38.586 mm) |
| Taper Angle | 1.7899° (1:16 taper ratio, 3/4"/ft) |
| Thread Depth (h = 0.8p) | 0.06957" (1.767 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: 1-1/2" (1.5000" / 38.10 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