What is the tap drill size for 1/16-27 NPT?

The tap drill for 1/16-27 NPT is E — 0.2500 in (6.350 mm). Taper pipe threads are tapped with a taper tap and sealed with compound or tape.

What is the pitch diameter of 1/16-27 NPT?

The basic pitch diameter of 1/16-27 NPT is 0.2812 in (7.142 mm).

What is the minor diameter of 1/16-27 NPT?

The basic minor diameter of 1/16-27 NPT is 0.2516 in (6.391 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 1/16-27 NPT?

1/16-27 NPT has 27 threads per inch, a pitch of 0.0370 in (0.941 mm).

What is the hand-tight engagement length (L₁) of 1/16-27 NPT?

The hand-tight engagement length L₁ for 1/16-27 NPT is 0.1600 in (4.064 mm), on a pipe outside diameter of 0.3125 in (7.938 mm).

NPT Taper Pipe Thread · 1/16-27 NPT

1/16-27 NPT Thread — Dimensions, Tap Drill & Clearance

https://shopmath.org/threads/npt/1-16 · data verified August 1, 2026

The tap drill for 1/16-27 NPT taper pipe thread is E — 0.2500 in (6.350 mm). Basic pitch diameter is 0.2812 in (7.142 mm) and basic minor diameter is 0.2516 in (6.391 mm).

Series: NPT Taper Pipe Thread
Designation: 1/16-27 NPT
TPI: 27
Standard: ASME B1.20.1, ASME B1.20.3; public-domain primary FED-STD-H28/7A

Tap drill · taper pipe tap

Drill Ø: 0.2500in
Drill Ø: 6.350mm

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 1/16-27 NPT

Basic thread dimensions — 1/16-27 NPT
Property	Inch	Millimetre
Basic major diameter	0.3125	7.938
Threads per inch	27	—
Pitch	0.0370	0.941
Basic pitch diameter	0.2812	7.142
Basic minor diameter	0.2516	6.391
Sharp V thread height (H)	0.0321	0.815

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 1/16-27 NPT

1/16-27 NPT 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.

Taper pipe thread geometry — 1/16-27 NPT
Property	Inch	Millimetre
Pipe outside diameter	0.3125	7.938
Taper on diameter, per foot	0.7500	19.050
Pitch Ø at end of pipe (E₀)	0.2712	6.888
Pitch Ø at hand-tight plane (E₁)	0.2812	7.142
Pitch Ø at effective plane (E₂)	0.2875	7.302
Hand-tight engagement (L₁)	0.1600	4.064
Effective thread length (L₂)	0.2611	6.632
Overall external thread length (L₄)	0.3896	9.896
Thread height (h)	0.0296	0.753
Sharp V height (H)	0.0321	0.815
Minor Ø at hand-tight plane	0.2516	6.391

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.

Other Thread Pitches in the Same Size as 1/16-27 NPT

A 1/16 fastener is not always 1/16-27 NPT. These are the other standard pitches cut on the same nominal size.

Other standard pitches at nominal size 1/16
Thread	Series	Pitch	Tap drill
1/16-27 NPTF	NPTF Dryseal Pipe Thread	27 TPI	E

Sources and Method for 1/16-27 NPT

Basic dimensions · 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 this data is built and checked →

How to Cite This 1/16-27 NPT Reference

Citation

ShopMath. "1/16-27 NPT Thread — Dimensions, Tap Drill & Clearance." ShopMath, verified August 1, 2026, https://shopmath.org/threads/npt/1-16

BibTeX

@misc{shopmath-threads-npt-1-16,
  title        = {1/16-27 NPT Thread — Dimensions, Tap Drill & Clearance},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/threads/npt/1-16}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/threads/npt/1-16

Common Questions About 1/16-27 NPT

What is the tap drill size for 1/16-27 NPT?: The tap drill for 1/16-27 NPT is E — 0.2500 in (6.350 mm). Taper pipe threads are tapped with a taper tap and sealed with compound or tape.
What is the pitch diameter of 1/16-27 NPT?: The basic pitch diameter of 1/16-27 NPT is 0.2812 in (7.142 mm).
What is the minor diameter of 1/16-27 NPT?: The basic minor diameter of 1/16-27 NPT is 0.2516 in (6.391 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 1/16-27 NPT?: 1/16-27 NPT has 27 threads per inch, a pitch of 0.0370 in (0.941 mm).
What is the hand-tight engagement length (L₁) of 1/16-27 NPT?: The hand-tight engagement length L₁ for 1/16-27 NPT is 0.1600 in (4.064 mm), on a pipe outside diameter of 0.3125 in (7.938 mm).

All NPT Taper Pipe Thread sizes · Every thread series