What is the tap drill size for 9/16"-12 UNC?

The tap drill for 9/16"-12 UNC is 31/64 — 0.4844 in (12.303 mm). That leaves 72.2% thread engagement with a cut tap.

What is the pitch diameter of 9/16"-12 UNC?

The basic pitch diameter of 9/16"-12 UNC is 0.5084 in (12.913 mm). For a class 2B thread it runs 0.5084 in (12.913 mm) to 0.5152 in (13.086 mm).

What is the minor diameter of 9/16"-12 UNC?

The basic minor diameter of 9/16"-12 UNC is 0.4723 in (11.996 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 9/16"-12 UNC?

9/16"-12 UNC has 12 threads per inch, a pitch of 0.0833 in (2.117 mm).

What is the tensile stress area of 9/16"-12 UNC?

The tensile stress area of 9/16"-12 UNC is 0.18194 in² (117.38 mm²). Multiply it by the fastener material's allowable stress to get a load.

Unified Coarse (UNC) · 9/16-12 UNC

9/16"-12 UNC Thread — Dimensions, Tap Drill & Clearance

https://shopmath.org/threads/unc/9-16-12 · data verified August 1, 2026

The tap drill for 9/16"-12 UNC is 31/64 — 0.4844 in (12.303 mm) — which leaves 72.2% thread engagement with a cut tap. Basic pitch diameter is 0.5084 in (12.913 mm) and basic minor diameter is 0.4723 in (11.996 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 Coarse (UNC)
Designation: 9/16-12 UNC
TPI: 12
Standard: ASME B1.1

Tap drill · 72.2% thread · cut tap

31/64

Drill Ø: 0.4844in
Drill Ø: 12.303mm

Assumes 75% thread engagement with a cut tap and a class 2B hole. That drill actually leaves 72.2% thread.

Basic Thread Dimensions for 9/16"-12 UNC

Basic thread dimensions — 9/16"-12 UNC
Property	Inch	Millimetre
Basic major diameter	0.5625	14.287
Threads per inch	12	—
Pitch	0.0833	2.117
Basic pitch diameter	0.5084	12.913
Basic minor diameter	0.4723	11.996
External thread root diameter	0.4633	11.768
Sharp V thread height (H)	0.0722	1.834

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 9/16"-12 UNC

Cut taps, from 50% to 85% thread engagement. The shop default is 75% — a 31/64 drill. Deeper engagement means more holding strength and more torque on the tap.

Tap drill sizes by thread engagement — 9/16"-12 UNC, cut tap
Property	Target hole Ø		Nearest standard drill			Property
Thread %	in	mm	Drill	in	mm	Actual thread %
50%	0.5084	12.913	33/64	0.5156	13.097	43.3
60%	0.4975	12.636	1/2	0.5000	12.700	57.7
65%	0.4921	12.499	31/64	0.4844	12.303	72.2
70%	0.4867	12.362	31/64	0.4844	12.303	72.2
75%default	0.4813	12.225	31/64	0.4844	12.303	72.2
80%	0.4759	12.088	15/32	0.4688	11.906	86.6
85%	0.4705	11.951	15/32	0.4688	11.906	86.6

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 9/16"-12 UNC

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 — 9/16"-12 UNC
Property	Class 2A		Class 3A
Limit	in	mm	in	mm
Major Ø max	0.5609	14.247	0.5625	14.287
Major Ø min	0.5495	13.957	0.5511	13.998
Pitch Ø max	0.5068	12.873	0.5084	12.913
Pitch Ø min	0.5016	12.741	0.5045	12.814
Pitch Ø tolerance	0.0052	0.132	0.0039	0.099
Minor Ø max	0.4527	11.499	0.4542	11.537
Minor Ø min	0.4475	11.367	0.4503	11.438
Allowance	0.0016	0.041	0.0000	0.000

Internal thread (nut / tapped hole) limits — 9/16"-12 UNC
Property	Class 2B		Class 3B
Limit	in	mm	in	mm
Major Ø max	0.5813	14.765	0.5796	14.722
Major Ø min	0.5625	14.287	0.5625	14.287
Pitch Ø max	0.5152	13.086	0.5135	13.043
Pitch Ø min	0.5084	12.913	0.5084	12.913
Pitch Ø tolerance	0.0068	0.173	0.0051	0.130
Minor Ø max	0.4903	12.454	0.4843	12.301
Minor Ø min	0.4723	11.996	0.4723	11.996
Allowance	0.0000	0.000	0.0000	0.000

Tensile Stress Area of 9/16"-12 UNC

The effective cross-section used to size a 9/16"-12 UNC fastener against a load. Multiply it by the material's allowable stress — the area itself carries no strength assumption.

Tensile stress area — 9/16"-12 UNC
Property	in²	mm²
Tensile stress area	0.18194	117.38

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

Other Thread Pitches in the Same Size as 9/16"-12 UNC

A 9/16 fastener is not always 9/16"-12 UNC. These are the other standard pitches cut on the same nominal size.

Other standard pitches at nominal size 9/16
Thread	Series	Pitch	Tap drill
9/16"-24 UNEF	Unified Extra Fine (UNEF)	24 TPI	33/64
9/16"-18 UNF	Unified Fine (UNF)	18 TPI	33/64

Sources and Method for 9/16"-12 UNC

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 9/16"-12 UNC Reference

Citation

ShopMath. "9/16"-12 UNC Thread — Dimensions, Tap Drill & Clearance." ShopMath, verified August 1, 2026, https://shopmath.org/threads/unc/9-16-12

BibTeX

@misc{shopmath-threads-unc-9-16-12,
  title        = {9/16"-12 UNC Thread — Dimensions, Tap Drill & Clearance},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/threads/unc/9-16-12}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/threads/unc/9-16-12

Common Questions About 9/16"-12 UNC

What is the tap drill size for 9/16"-12 UNC?: The tap drill for 9/16"-12 UNC is 31/64 — 0.4844 in (12.303 mm). That leaves 72.2% thread engagement with a cut tap.
What is the pitch diameter of 9/16"-12 UNC?: The basic pitch diameter of 9/16"-12 UNC is 0.5084 in (12.913 mm). For a class 2B thread it runs 0.5084 in (12.913 mm) to 0.5152 in (13.086 mm).
What is the minor diameter of 9/16"-12 UNC?: The basic minor diameter of 9/16"-12 UNC is 0.4723 in (11.996 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 9/16"-12 UNC?: 9/16"-12 UNC has 12 threads per inch, a pitch of 0.0833 in (2.117 mm).
What is the tensile stress area of 9/16"-12 UNC?: The tensile stress area of 9/16"-12 UNC is 0.18194 in² (117.38 mm²). Multiply it by the fastener material's allowable stress to get a load.

All Unified Coarse (UNC) sizes · Every thread series