NPTF Dryseal Pipe Thread · 1 1/2-11.5 NPTF
1 1/2-11.5 NPTF Thread — Dimensions, Tap Drill & Clearance
https://shopmath.org/threads/nptf/1-1-2 · data verified August 1, 2026
The tap drill for 1 1/2-11.5 NPTF taper pipe thread is 1 — 1.0000 in (25.400 mm). Basic pitch diameter is 1.8223 in (46.287 mm) and basic minor diameter is 1.7528 in (44.521 mm).
- Series
- NPTF Dryseal Pipe Thread
- Designation
- 1 1/2-11.5 NPTF
- TPI
- 12
- Standard
- ASME B1.20.1, ASME B1.20.3; public-domain primary FED-STD-H28/7A
Tap drill · taper pipe tap
1
- Drill Ø
- 1.0000in
- Drill Ø
- 25.400mm
NPT and NPTF holes are drilled straight and cut with a taper tap. The standard assumes a sealing compound or tape on the joint.
Basic Thread Dimensions for 1 1/2-11.5 NPTF
| Property | Inch | Millimetre |
|---|---|---|
| Basic major diameter | 1.9000 | 48.260 |
| Threads per inch | 12 | — |
| Pitch | 0.0870 | 2.209 |
| Basic pitch diameter | 1.8223 | 46.287 |
| Basic minor diameter | 1.7528 | 44.521 |
| Sharp V thread height (H) | 0.0753 | 1.913 |
Threads per inch has no millimetre counterpart — metric threads are specified by pitch instead. Basic dimensions are the theoretical values before any tolerance class is applied.
Taper Pipe Thread Geometry for 1 1/2-11.5 NPTF
1 1/2-11.5 NPTF is a taper thread: the diameter changes along the thread, so every diameter below is stated at a named plane. The taper is 0.7500 in per foot on diameter.
| Property | Inch | Millimetre |
|---|---|---|
| Pipe outside diameter | 1.9000 | 48.260 |
| Taper on diameter, per foot | 0.7500 | 19.050 |
| Pitch Ø at end of pipe (E₀) | 1.7961 | 45.621 |
| Pitch Ø at hand-tight plane (E₁) | 1.8223 | 46.287 |
| Pitch Ø at effective plane (E₂) | 1.8413 | 46.769 |
| Hand-tight engagement (L₁) | 0.4200 | 10.668 |
| Effective thread length (L₂) | 0.7235 | 18.377 |
| Overall external thread length (L₄) | 1.0252 | 26.040 |
| Thread height (h) | 0.0696 | 1.767 |
| Sharp V height (H) | 0.0753 | 1.913 |
| Minor Ø at hand-tight plane | 1.7528 | 44.521 |
ASME B1.20.1 publishes these dimensions in inches only; the millimetre column is an exact conversion (1 in = 25.4 mm by definition). L₁ is the hand-tight engagement length and is tabulated in the standard, not derived.
Sources and Method for 1 1/2-11.5 NPTF
- Basic dimensionscomputed+compiled
ASME B1.20.1 taper pipe thread formulas; E0 and L2 reproduced to 5 decimals in docs/research/data-sourcing.md §3.3. Public-domain primary: FED-STD-H28/7A (1984).; pipe OD / tpi / L1 / L4: ASME B1.20.1 pipe OD / tpi / L1 / L4 via Wikipedia National pipe thread (CC BY-SA 4.0); OD and tpi cross-checked against FreeCAD FeatureHole.cpp NPT block (LGPL-2.1+). NPTF shares the NPT taper geometry; dryseal crest/root truncation limits are NOT included (single-source only — see generator header).
Verified against Wikipedia National pipe thread standard-sizes table (CC BY-SA 4.0) — 98 checks passed to 1e-5 in
Part computed from the standard's formulas, part compiled from agreeing public sources.
- Taper pipe geometrycomputed+compiled
ASME B1.20.1 taper pipe thread formulas; E0 and L2 reproduced to 5 decimals in docs/research/data-sourcing.md §3.3. Public-domain primary: FED-STD-H28/7A (1984).; pipe OD / tpi / L1 / L4: ASME B1.20.1 pipe OD / tpi / L1 / L4 via Wikipedia National pipe thread (CC BY-SA 4.0); OD and tpi cross-checked against FreeCAD FeatureHole.cpp NPT block (LGPL-2.1+)
Verified against Wikipedia National pipe thread standard-sizes table (CC BY-SA 4.0) — 98 checks passed to 1e-5 in
Part computed from the standard's formulas, part compiled from agreeing public sources.
- Assumptions
- NPT threads are not a seal on their own — the standard assumes a sealing compound or tape on the joint.
- Dataset scope: L1 is tabulated, not derivable (data-sourcing.md §3.3). EXCLUDED: NPTF crest/root truncation limits (single-sourced), NPSM/NPSC/NPSF straight pipe threads, BSPT/BSPP.
- Data last verified
- August 1, 2026
How to Cite This 1 1/2-11.5 NPTF Reference
Citation
ShopMath. "1 1/2-11.5 NPTF Thread — Dimensions, Tap Drill & Clearance." ShopMath, verified August 1, 2026, https://shopmath.org/threads/nptf/1-1-2
BibTeX
@misc{shopmath-threads-nptf-1-1-2,
title = {1 1/2-11.5 NPTF Thread — Dimensions, Tap Drill & Clearance},
author = {{ShopMath}},
year = {2026},
howpublished = {\url{https://shopmath.org/threads/nptf/1-1-2}},
note = {Data verified 2026-08-01}
}Permanent URL
https://shopmath.org/threads/nptf/1-1-2
Common Questions About 1 1/2-11.5 NPTF
What is the tap drill size for 1 1/2-11.5 NPTF?
- The tap drill for 1 1/2-11.5 NPTF is 1 — 1.0000 in (25.400 mm). Taper pipe threads are tapped with a taper tap and sealed with compound or tape.
What is the pitch diameter of 1 1/2-11.5 NPTF?
- The basic pitch diameter of 1 1/2-11.5 NPTF is 1.8223 in (46.287 mm).
What is the minor diameter of 1 1/2-11.5 NPTF?
- The basic minor diameter of 1 1/2-11.5 NPTF is 1.7528 in (44.521 mm). That is the theoretical root of the internal thread, not the drilled hole size — see the tap drill table for the hole to drill.
What is the thread pitch of 1 1/2-11.5 NPTF?
- 1 1/2-11.5 NPTF has 12 threads per inch, a pitch of 0.0870 in (2.209 mm).
What is the hand-tight engagement length (L₁) of 1 1/2-11.5 NPTF?
- The hand-tight engagement length L₁ for 1 1/2-11.5 NPTF is 0.4200 in (10.668 mm), on a pipe outside diameter of 1.9000 in (48.260 mm).