---
type: "thread"
name: "#6-32 UNC"
designation: "#6-32 UNC"
series: "unc"
series_name: "Unified Coarse (UNC)"
system: "unified"
size_label: "#6"
tpi: 32
pitch_in: 0.03125
pitch_mm: 0.7938
basic_major_dia_in: 0.138
basic_major_dia_mm: 3.5052
basic_pitch_dia_in: 0.1177
basic_pitch_dia_mm: 2.9896
basic_minor_dia_in: 0.1042
basic_minor_dia_mm: 2.6467
tap_drill: "#36"
tap_drill_dia_in: 0.1065
tap_drill_dia_mm: 2.7051
tap_drill_thread_pct: 77.6
clearance_normal_drill: "#19"
tensile_stress_area_sqin: 0.009085
tensile_stress_area_sqmm: 5.861
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/unc/6-32
---

# #6-32 UNC Thread — Dimensions, Tap Drill & Clearance

The tap drill for #6-32 UNC is #36 — 0.1065 in (2.705 mm) — which leaves 77.6% thread engagement with a cut tap. Basic pitch diameter is 0.1177 in (2.990 mm) and basic minor diameter is 0.1042 in (2.647 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**: #6-32 UNC
- **Threads per inch**: 32
- **Tap drill**: #36
- **Standard**: ASME B1.1 (reference values based on the ASME B1.1 system; not a compliance claim)

## Basic Thread Dimensions for #6-32 UNC

| Property | Inch | Millimetre |
| --- | --- | --- |
| Basic major diameter | 0.1380 | 3.505 |
| Threads per inch | 32 | — |
| Pitch | 0.0313 | 0.794 |
| Basic pitch diameter | 0.1177 | 2.990 |
| Basic minor diameter | 0.1042 | 2.647 |
| External thread root diameter | 0.1008 | 2.560 |
| 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 #6-32 UNC

Cut taps, from 50% to 85% thread engagement. The shop default is 75% — a #36 drill.

| Thread % | Target hole Ø (in) | Target hole Ø (mm) | Drill | Drill Ø (in) | Drill Ø (mm) | Actual thread % |
| --- | --- | --- | --- | --- | --- | --- |
| 50% | 0.1177 | 2.990 | #32 | 0.1160 | 2.946 | 54.2 |
| 60% | 0.1136 | 2.885 | #33 | 0.1130 | 2.870 | 61.6 |
| 65% | 0.1116 | 2.835 | #34 | 0.1110 | 2.819 | 66.5 |
| 70% | 0.1096 | 2.784 | 7/64 | 0.1094 | 2.778 | 70.5 |
| 75% (default) | 0.1076 | 2.733 | #36 | 0.1065 | 2.705 | 77.6 |
| 80% | 0.1055 | 2.680 | #36 | 0.1065 | 2.705 | 77.6 |
| 85% | 0.1035 | 2.629 | #37 | 0.1040 | 2.642 | 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._

## Clearance Hole Sizes for #6-32 UNC

The through-hole a #6-32 UNC fastener passes freely, not the tapped hole.

| Fit | Drill | Hole Ø (in) | Hole Ø (mm) | Use |
| --- | --- | --- | --- | --- |
| Close | #24 | 0.1535 | 3.899 | Located joints, dowelled assemblies |
| Normal | #19 | 0.1693 | 4.300 | General assembly — the default |
| Loose | #13 | 0.1850 | 4.699 | Slotted or adjustable joints, weldments |

_Clearance holes per ISO 273 (metric) and ASME B18.2.8 (inch)._

## Thread Class Limits for #6-32 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

| Limit | Class 2A (in) | Class 2A (mm) | Class 3A (in) | Class 3A (mm) |
| --- | --- | --- | --- | --- |
| Major Ø max | 0.1372 | 3.485 | 0.1380 | 3.505 |
| Major Ø min | 0.1312 | 3.333 | 0.1320 | 3.353 |
| Pitch Ø max | 0.1169 | 2.969 | 0.1177 | 2.990 |
| Pitch Ø min | 0.1140 | 2.896 | 0.1156 | 2.936 |
| Pitch Ø tolerance | 0.0028 | 0.071 | 0.0021 | 0.053 |
| Minor Ø max | 0.0966 | 2.454 | 0.0974 | 2.474 |
| Minor Ø min | 0.0937 | 2.380 | 0.0953 | 2.421 |
| Allowance | 0.0008 | 0.020 | 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 | 0.1462 | 3.713 | 0.1453 | 3.691 |
| Major Ø min | 0.1380 | 3.505 | 0.1380 | 3.505 |
| Pitch Ø max | 0.1214 | 3.084 | 0.1205 | 3.061 |
| Pitch Ø min | 0.1177 | 2.990 | 0.1177 | 2.990 |
| Pitch Ø tolerance | 0.0037 | 0.094 | 0.0028 | 0.071 |
| Minor Ø max | 0.1139 | 2.893 | 0.1139 | 2.893 |
| Minor Ø min | 0.1042 | 2.647 | 0.1042 | 2.647 |
| Allowance | 0.0000 | 0.000 | 0.0000 | 0.000 |

## Tensile Stress Area of #6-32 UNC

| Property | in² | mm² |
| --- | --- | --- |
| Tensile stress area | 0.00908 | 5.86 |

The effective cross-section used to size a #6-32 UNC 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 #6-32 UNC

A #6 fastener is not always #6-32 UNC. These are the other standard pitches cut on the same nominal size.

| Thread | Series | Pitch | Tap drill |
| --- | --- | --- | --- |
| [#6-40 UNF](https://shopmath.org/threads/unf/6-40.md) | Unified Fine (UNF) | 40 TPI | #33 |

## Sources and Method for #6-32 UNC

### 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 #6-32 UNC

### What is the tap drill size for #6-32 UNC?

The tap drill for #6-32 UNC is #36 — 0.1065 in (2.705 mm). That leaves 77.6% thread engagement with a cut tap.

### What is the pitch diameter of #6-32 UNC?

The basic pitch diameter of #6-32 UNC is 0.1177 in (2.990 mm). For a class 2B thread it runs 0.1177 in (2.990 mm) to 0.1214 in (3.084 mm).

### What is the minor diameter of #6-32 UNC?

The basic minor diameter of #6-32 UNC is 0.1042 in (2.647 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 #6-32 UNC?

#6-32 UNC has 32 threads per inch, a pitch of 0.0313 in (0.794 mm).

### What size clearance hole does a #6-32 UNC fastener need?

close fit #24 (0.1535 in (3.899 mm)), normal fit #19 (0.1693 in (4.300 mm)), loose fit #13 (0.1850 in (4.699 mm)). The normal fit is the general-assembly default.

### What is the tensile stress area of #6-32 UNC?

The tensile stress area of #6-32 UNC is 0.00908 in² (5.86 mm²). Multiply it by the fastener material's allowable stress to get a load.

## Related pages

- Smaller in Unified Coarse (UNC): [#5-40 UNC](https://shopmath.org/threads/unc/5-40.md) — tap drill #38
- Larger in Unified Coarse (UNC): [#8-32 UNC](https://shopmath.org/threads/unc/8-32.md) — tap drill #29
- All Unified Coarse (UNC) sizes: [Unified Coarse (UNC) thread chart](https://shopmath.org/threads/unc.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/unc/6-32) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*