1/4" NPT Thread Specifications
Complete dimensions for 1/4" NPT (National Pipe Taper) thread per ASME B1.20.1. TPI: 18, Pitch: 0.05556" (1.411 mm). Taper: 1 in 16 on diameter (3/4" per foot).
Thread Dimensions
| Designation | 1/4" NPT |
| Nominal Pipe Size | 1/4" |
| TPI | 18 |
| Pitch | 0.05556" (1.411 mm) |
| Outside Diameter | 0.5400" (13.72 mm) |
| Pitch Diameter at E0 (hand-tight) | 0.47739" (12.126 mm) |
| Pitch Diameter at E1 (wrench makeup) | 0.49163" (12.487 mm) |
| Minor Diameter at E0 | 0.44929" (11.412 mm) |
| Taper Angle | 1.7899° (1:16 taper ratio, 3/4"/ft) |
| Thread Depth (h = 0.8p) | 0.04444" (1.129 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: 7/16" (0.4375" / 11.11 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