---
type: "thread"
name: "#12-32 UNEF"
designation: "#12-32 UNEF"
series: "unef"
series_name: "Unified Extra Fine (UNEF)"
system: "unified"
size_label: "#12"
tpi: 32
pitch_in: 0.03125
pitch_mm: 0.7938
basic_major_dia_in: 0.216
basic_major_dia_mm: 5.4864
basic_pitch_dia_in: 0.1957
basic_pitch_dia_mm: 4.9708
basic_minor_dia_in: 0.1822
basic_minor_dia_mm: 4.6279
tap_drill: "#13"
tap_drill_dia_in: 0.185
tap_drill_dia_mm: 4.699
tap_drill_thread_pct: 76.4
tensile_stress_area_sqin: 0.027041
tensile_stress_area_sqmm: 17.446
internal_class_assumed: "2B"
standard: "ASME B1.1 (reference values based on the ASME B1.1 system; not a compliance claim)"
verified: "August 1, 2026"
url: https://shopmath.org/threads/unef/12-32
---

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

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
- **Threads per inch**: 32
- **Tap drill**: #13
- **Standard**: ASME B1.1 (reference values based on the ASME B1.1 system; not a compliance claim)

## Basic Thread Dimensions for #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 |

_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.

| Thread % | Target hole Ø (in) | Target hole Ø (mm) | Drill | Drill Ø (in) | Drill Ø (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._

> **This differs from the traditional chart.** 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. Computed recommendation: #13 (0.1850 in, 76.4% thread). Traditional published chart: 3/16 (0.1880 in, 69.0% thread).

## 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

| Limit | Class 2A (in) | Class 2A (mm) | Class 3A (in) | Class 3A (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

| Limit | Class 2B (in) | Class 2B (mm) | Class 3B (in) | Class 3B (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

| Property | in² | mm² |
| --- | --- | --- |
| Tensile stress area | 0.02704 | 17.45 |

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.

## 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.

| Thread | Series | Pitch | Tap drill |
| --- | --- | --- | --- |
| [#12-28 UNF](https://shopmath.org/threads/unf/12-28.md) | Unified Fine (UNF) | 28 TPI | #14 |
| [#12-24 UNC](https://shopmath.org/threads/unc/12-24.md) | Unified Coarse (UNC) | 24 TPI | #16 |

## Sources and Method for #12-32 UNEF

### Basic dimensions

- **Source**: 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)
- **Method**: computed
- **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

### Tap drill sizes

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

### Class limits

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

### Formulas

**Tap drill hole diameter, inch threads**

```text
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**

```text
%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**

```text
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 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

## 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.

## Related pages

- Larger in Unified Extra Fine (UNEF): [1/4"-32 UNEF](https://shopmath.org/threads/unef/1-4-32.md) — tap drill 7/32
- All Unified Extra Fine (UNEF) sizes: [Unified Extra Fine (UNEF) thread chart](https://shopmath.org/threads/unef.md)
- Every thread series: [Screw thread reference](https://shopmath.org/threads.md)
- Cross-series chart: [Tap drill chart](https://shopmath.org/charts/tap-drill.md)

---

*Source: [ShopMath](https://shopmath.org/threads/unef/12-32) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*