MAN4MACHINENPTR
National Pipe Taper Railing
Dimensionally an NPT taper, retasked for modular pipe railing and structural fittings rather than fluid systems. It's classed here as hybrid because the geometry is fully tapered but the design intent is purely mechanical: a strong, self-tightening joint, not a pressure seal.
- Standard
- ANSI/ASME B1.20.1
- Flank angle
- 60° included
- Taper
- 1 : 16 on diameter
- Sealing
- Mechanical engagement only -- the joint is not intended to hold pressure.
Thread profile
A 60° included flank angle with a flat-truncated crest and root -- the single fastest way to tell a Unified/American pipe thread from the other family by eye.
Size chart
| Nominal | TPI | Pitch | Major Ø | Pitch Ø | Minor Ø | Tap drill |
|---|---|---|---|---|---|---|
| 1/16 | 27 | 0.0370" | 0.3125" | 0.2884" | 0.2644" | J (0.2764") |
| 1/8 | 27 | 0.0370" | 0.4050" | 0.3809" | 0.3569" | U (0.3689") |
| 1/4 | 18 | 0.0556" | 0.5400" | 0.5039" | 0.4678" | 31/64" (0.4859") |
| 3/8 | 18 | 0.0556" | 0.6750" | 0.6389" | 0.6028" | 5/8" (0.6209") |
| 1/2 | 14 | 0.0714" | 0.8400" | 0.7936" | 0.7472" | 49/64" (0.7704") |
| 3/4 | 14 | 0.0714" | 1.0500" | 1.0036" | 0.9572" | 63/64" (0.9804") |
| 1 | 11.50 | 0.0870" | 1.3150" | 1.2585" | 1.2020" | 1-15/64" (1.2303") |
| 1-1/4 | 11.50 | 0.0870" | 1.6600" | 1.6035" | 1.5470" | 1-37/64" (1.5753") |
| 1-1/2 | 11.50 | 0.0870" | 1.9000" | 1.8435" | 1.7870" | 1-13/16" (1.8153") |
| 2 | 11.50 | 0.0870" | 2.3750" | 2.3185" | 2.2620" | 2" (2.2903") |
| 2-1/2 | 8 | 0.1250" | 2.8750" | 2.7938" | 2.7126" | 2" (2.7532") |
| 3 | 8 | 0.1250" | 3.5000" | 3.4188" | 3.3376" | 2" (3.3782") |
| 4 | 8 | 0.1250" | 4.5000" | 4.4188" | 4.3376" | 2" (4.3782") |
Tap drill calculator
NPTR is hybrid: engagement here depends on how far the joint is driven onto the taper, not diameter alone. Treat this as a straight-thread approximation and check ANSI/ASME B1.20.1 or your tap manufacturer’s chart before cutting production parts.
Calculated live
- Pitch
- 0.0370"
- Pitch diameter (basic)
- 0.2884"
- Minor diameter (basic)
- 0.2644"
- Clearance drill (normal)
- 11/32" (0.3438")
Comparing against another standard? Open the universal calculator →