What is the tap drill size for #12-32 UNEF?

The tap drill for #12-32 UNEF is #13 — 0.1850 in (4.699 mm). That leaves 76.4% thread engagement with a cut tap.

What is the pitch diameter of #12-32 UNEF?

The basic pitch diameter of #12-32 UNEF is 0.1957 in (4.971 mm). For a class 2B thread it runs 0.1957 in (4.971 mm) to 0.1998 in (5.075 mm).

What is the minor diameter of #12-32 UNEF?

The basic minor diameter of #12-32 UNEF is 0.1822 in (4.628 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 #12-32 UNEF?

#12-32 UNEF has 32 threads per inch, a pitch of 0.0313 in (0.794 mm).

What is the tensile stress area of #12-32 UNEF?

The tensile stress area of #12-32 UNEF is 0.02704 in² (17.45 mm²). Multiply it by the fastener material's allowable stress to get a load.

Why does the #12-32 UNEF tap drill here differ from the chart on the wall?

Computed 75% target 0.1856 in. Nearest standard drill is #13 (0.185 in, off by 0.0006 in); the traditional published chart lists 3/16 (0.188 in, off by 0.0024 in, 69% thread). Both are shown; neither overrides the other.

Unified Extra Fine (UNEF) · #12-32 UNEF

#12-32 UNEF Thread — Dimensions, Tap Drill & Clearance

https://shopmath.org/threads/unef/12-32 · data verified August 1, 2026

The tap drill for #12-32 UNEF is #13 — 0.1850 in (4.699 mm) — which leaves 76.4% thread engagement with a cut tap. Basic pitch diameter is 0.1957 in (4.971 mm) and basic minor diameter is 0.1822 in (4.628 mm). Tapped-hole figures on this page assume a class 2B thread; drill sizes for 50–85% engagement are in the tap drill table below.

Series: Unified Extra Fine (UNEF)
Designation: #12-32 UNEF
TPI: 32
Standard: ASME B1.1

Tap drill · 76.4% thread · cut tap

#13

Drill Ø: 0.1850in
Drill Ø: 4.699mm

Assumes 75% thread engagement with a cut tap and a class 2B hole. That drill actually leaves 76.4% thread.

Basic Thread Dimensions for #12-32 UNEF

Basic thread dimensions — #12-32 UNEF
Property	Inch	Millimetre
Basic major diameter	0.2160	5.486
Threads per inch	32	—
Pitch	0.0313	0.794
Basic pitch diameter	0.1957	4.971
Basic minor diameter	0.1822	4.628
External thread root diameter	0.1788	4.542
Sharp V thread height (H)	0.0271	0.688

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.

Tap Drill Sizes for #12-32 UNEF

Cut taps, from 50% to 85% thread engagement. The shop default is 75% — a #13 drill. Deeper engagement means more holding strength and more torque on the tap.

Tap drill sizes by thread engagement — #12-32 UNEF, cut tap
Property	Target hole Ø		Nearest standard drill			Property
Thread %	in	mm	Drill	in	mm	Actual thread %
50%	0.1957	4.971	#9	0.1960	4.978	49.3
60%	0.1916	4.867	#11	0.1910	4.851	61.6
65%	0.1896	4.816	#12	0.1890	4.801	66.5
70%	0.1876	4.765	3/16	0.1875	4.763	70.2
75%default	0.1856	4.714	#13	0.1850	4.699	76.4
80%	0.1835	4.661	#13	0.1850	4.699	76.4
85%	0.1815	4.610	#14	0.1820	4.623	83.8

Target hole Ø is the theoretical hole for the stated engagement. The drill column is the nearest size in the standard number/letter/fractional/metric index, and actual thread % is what that real drill produces — the number that matters at the machine. Values are for cut taps. Tapped-hole figures assume a class 2B hole.

Thread Class Limits for #12-32 UNEF

Manufacturing limits for classes 2B, 3B, 2A, 3A. A gauge reading outside these bands is a reject, not a judgement call.

External thread (bolt / screw) limits — #12-32 UNEF
Property	Class 2A		Class 3A
Limit	in	mm	in	mm
Major Ø max	0.2150	5.461	0.2160	5.486
Major Ø min	0.2091	5.311	0.2100	5.334
Pitch Ø max	0.1947	4.945	0.1957	4.971
Pitch Ø min	0.1916	4.867	0.1933	4.910
Pitch Ø tolerance	0.0032	0.081	0.0024	0.061
Minor Ø max	0.1744	4.430	0.1754	4.455
Minor Ø min	0.1713	4.351	0.1730	4.394
Allowance	0.0010	0.025	0.0000	0.000

Internal thread (nut / tapped hole) limits — #12-32 UNEF
Property	Class 2B		Class 3B
Limit	in	mm	in	mm
Major Ø max	0.2246	5.705	0.2236	5.679
Major Ø min	0.2160	5.486	0.2160	5.486
Pitch Ø max	0.1998	5.075	0.1988	5.050
Pitch Ø min	0.1957	4.971	0.1957	4.971
Pitch Ø tolerance	0.0041	0.104	0.0031	0.079
Minor Ø max	0.1896	4.816	0.1895	4.813
Minor Ø min	0.1822	4.628	0.1822	4.628
Allowance	0.0000	0.000	0.0000	0.000

Tensile Stress Area of #12-32 UNEF

The effective cross-section used to size a #12-32 UNEF fastener against a load. Multiply it by the material's allowable stress — the area itself carries no strength assumption.

Tensile stress area — #12-32 UNEF
Property	in²	mm²
Tensile stress area	0.02704	17.45

The formula this value comes from is in the sources section below.

Other Thread Pitches in the Same Size as #12-32 UNEF

A #12 fastener is not always #12-32 UNEF. These are the other standard pitches cut on the same nominal size.

Other standard pitches at nominal size #12
Thread	Series	Pitch	Tap drill
#12-28 UNF	Unified Fine (UNF)	28 TPI	#14
#12-24 UNC	Unified Coarse (UNC)	24 TPI	#16

Sources and Method for #12-32 UNEF

Basic dimensionscomputed

NBS Handbook H28 (1969) Part I §§6-7 (public domain, 17 U.S.C. 105); normative modern reference ASME B1.1; series membership: Series membership: threadlib UIS_thread.csv (BSD-3-Clause); cross-checked against NBS H28 (1969) Part I Table 2.21; clearance holes: ISO 273 (metric) and ASME B18.2.8 (inch) via FreeCAD FeatureHole.cpp (LGPL-2.1+), cross-checked against bd_warehouse clearance_hole_sizes.csv (Apache-2.0)

Verified against NBS H28 (1969) Part I, Table 2.21 (public domain); cross-checked against FreeCAD CAM thread tables (LGPL-2.1+) — 1064 checks passed at 0.0001 in

Computed from the standard's formulas, then checked against published tables.

Tap drill sizescomputed

Machinery's Handbook %-thread formula (geometry-derived); nearest-standard-drill-to-75% rule verified at 36/39 published chart rows in docs/research/data-sourcing.md §3.4

Verified against Wikipedia Unified Thread Standard, preferred cutting tap drill size columns (CC BY-SA 4.0) — 36/39 published UNC+UNF rows reproduced

Computed from the standard's formulas, then checked against published tables.

Class limitscomputed

NBS Handbook H28 (1969) Part I §§6-7 (public domain, 17 U.S.C. 105); normative modern reference ASME B1.1

Verified against NBS H28 (1969) Part I, Table 2.21 (public domain); cross-checked against FreeCAD CAM thread tables (LGPL-2.1+) — 1064 checks passed at 0.0001 in

Computed from the standard's formulas, then checked against published tables.

Formula

Tap drill hole diameter, inch threads

hole Ø  =  D − (%thread ÷ 100) × (1.29904 ÷ n)

  D = basic major diameter (in)
  n = threads per inch

1.29904 = 2 × 0.64952, twice the engaged thread height per side on the 60° Unified profile.

Actual thread engagement of the chosen drill

%thread  =  (D − drill Ø) × n ÷ 1.29904 × 100

The drill column rounds to a real drill; this is the engagement that drill actually leaves.

Tensile stress area, Unified inch threads

At  =  0.7854 × (D − 0.9743 ÷ n)²

ASME B1.1 / NBS H28 form. Reproduces the stored value exactly for this thread.

Assumptions

The headline tap drill assumes 75% thread engagement, the general shop default. Every other engagement from 50% to 85% is in the tap drill table — change the assumption and the number moves.
Tap drill figures are for cut taps. Drill diameters are nominal; a worn or run-out drill cuts oversize and reduces engagement further.
Tapped-hole figures assume a class 2B internal thread, the general-purpose fit.
Dataset scope: Le = 1D for UNC/UNF, 9P for UNEF — determined empirically against H28 Table 2.21, resolving data-sourcing.md open item 5. EXCLUDED: form (roll) tap drills, class 1A/1B limits, class 1AR allowances, constant-pitch UN series.

Data last verified

August 1, 2026

How this data is built and checked →

How to Cite This #12-32 UNEF Reference

Citation

ShopMath. "#12-32 UNEF Thread — Dimensions, Tap Drill & Clearance." ShopMath, verified August 1, 2026, https://shopmath.org/threads/unef/12-32

BibTeX

@misc{shopmath-threads-unef-12-32,
  title        = {#12-32 UNEF Thread — Dimensions, Tap Drill & Clearance},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/threads/unef/12-32}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/threads/unef/12-32

Common Questions About #12-32 UNEF

What is the tap drill size for #12-32 UNEF?: The tap drill for #12-32 UNEF is #13 — 0.1850 in (4.699 mm). That leaves 76.4% thread engagement with a cut tap.
What is the pitch diameter of #12-32 UNEF?: The basic pitch diameter of #12-32 UNEF is 0.1957 in (4.971 mm). For a class 2B thread it runs 0.1957 in (4.971 mm) to 0.1998 in (5.075 mm).
What is the minor diameter of #12-32 UNEF?: The basic minor diameter of #12-32 UNEF is 0.1822 in (4.628 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 #12-32 UNEF?: #12-32 UNEF has 32 threads per inch, a pitch of 0.0313 in (0.794 mm).
What is the tensile stress area of #12-32 UNEF?: The tensile stress area of #12-32 UNEF is 0.02704 in² (17.45 mm²). Multiply it by the fastener material's allowable stress to get a load.
Why does the #12-32 UNEF tap drill here differ from the chart on the wall?: Computed 75% target 0.1856 in. Nearest standard drill is #13 (0.185 in, off by 0.0006 in); the traditional published chart lists 3/16 (0.188 in, off by 0.0024 in, 69% thread). Both are shown; neither overrides the other.

All Unified Extra Fine (UNEF) sizes · Every thread series