---
type: "thread"
name: "3/4\"-10 UNC"
designation: "3/4-10 UNC"
series: "unc"
series_name: "Unified Coarse (UNC)"
system: "unified"
size_label: "3/4"
tpi: 10
pitch_in: 0.1
pitch_mm: 2.54
basic_major_dia_in: 0.75
basic_major_dia_mm: 19.05
basic_pitch_dia_in: 0.685
basic_pitch_dia_mm: 17.399
basic_minor_dia_in: 0.6417
basic_minor_dia_mm: 16.2992
tap_drill: "21/32"
tap_drill_dia_in: 0.65625
tap_drill_dia_mm: 16.6688
tap_drill_thread_pct: 72.2
clearance_normal_drill: "51/64"
tensile_stress_area_sqin: 0.334461
tensile_stress_area_sqmm: 215.781
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/3-4-10
---

# 3/4"-10 UNC Thread — Dimensions, Tap Drill & Clearance

The tap drill for 3/4"-10 UNC is 21/32 — 0.6563 in (16.669 mm) — which leaves 72.2% thread engagement with a cut tap. Basic pitch diameter is 0.6850 in (17.399 mm) and basic minor diameter is 0.6417 in (16.299 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**: 3/4-10 UNC
- **Threads per inch**: 10
- **Tap drill**: 21/32
- **Standard**: ASME B1.1 (reference values based on the ASME B1.1 system; not a compliance claim)

## Basic Thread Dimensions for 3/4"-10 UNC

| Property | Inch | Millimetre |
| --- | --- | --- |
| Basic major diameter | 0.7500 | 19.050 |
| Threads per inch | 10 | — |
| Pitch | 0.1000 | 2.540 |
| Basic pitch diameter | 0.6850 | 17.399 |
| Basic minor diameter | 0.6417 | 16.299 |
| External thread root diameter | 0.6309 | 16.025 |
| Sharp V thread height (H) | 0.0866 | 2.200 |

_Basic dimensions are the theoretical values before any tolerance class is applied._

## Tap Drill Sizes for 3/4"-10 UNC

Cut taps, from 50% to 85% thread engagement. The shop default is 75% — a 21/32 drill.

| Thread % | Target hole Ø (in) | Target hole Ø (mm) | Drill | Drill Ø (in) | Drill Ø (mm) | Actual thread % |
| --- | --- | --- | --- | --- | --- | --- |
| 50% | 0.6850 | 17.399 | 11/16 | 0.6875 | 17.462 | 48.1 |
| 60% | 0.6721 | 17.071 | 43/64 | 0.6719 | 17.066 | 60.1 |
| 65% | 0.6656 | 16.906 | 43/64 | 0.6719 | 17.066 | 60.1 |
| 70% | 0.6591 | 16.741 | 21/32 | 0.6563 | 16.669 | 72.2 |
| 75% (default) | 0.6526 | 16.576 | 21/32 | 0.6563 | 16.669 | 72.2 |
| 80% | 0.6461 | 16.411 | 41/64 | 0.6406 | 16.272 | 84.2 |
| 85% | 0.6396 | 16.246 | 41/64 | 0.6406 | 16.272 | 84.2 |

_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 3/4"-10 UNC

The through-hole a 3/4"-10 UNC fastener passes freely, not the tapped hole.

| Fit | Drill | Hole Ø (in) | Hole Ø (mm) | Use |
| --- | --- | --- | --- | --- |
| Close | 49/64 | 0.7795 | 19.799 | Located joints, dowelled assemblies |
| Normal | 51/64 | 0.8110 | 20.599 | General assembly — the default |
| Loose | 57/64 | 0.9055 | 23.000 | Slotted or adjustable joints, weldments |

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

## Thread Class Limits for 3/4"-10 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 | 0.7482 | 19.004 | 0.7500 | 19.050 |
| Major Ø min | 0.7353 | 18.677 | 0.7371 | 18.722 |
| Pitch Ø max | 0.6833 | 17.356 | 0.6850 | 17.399 |
| Pitch Ø min | 0.6774 | 17.206 | 0.6806 | 17.287 |
| Pitch Ø tolerance | 0.0059 | 0.150 | 0.0044 | 0.112 |
| Minor Ø max | 0.6183 | 15.705 | 0.6201 | 15.751 |
| Minor Ø min | 0.6124 | 15.555 | 0.6157 | 15.639 |
| Allowance | 0.0018 | 0.046 | 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 | 0.7721 | 19.611 | 0.7702 | 19.563 |
| Major Ø min | 0.7500 | 19.050 | 0.7500 | 19.050 |
| Pitch Ø max | 0.6927 | 17.595 | 0.6908 | 17.546 |
| Pitch Ø min | 0.6850 | 17.399 | 0.6850 | 17.399 |
| Pitch Ø tolerance | 0.0077 | 0.196 | 0.0057 | 0.145 |
| Minor Ø max | 0.6627 | 16.833 | 0.6545 | 16.624 |
| Minor Ø min | 0.6417 | 16.299 | 0.6417 | 16.299 |
| Allowance | 0.0000 | 0.000 | 0.0000 | 0.000 |

## Tensile Stress Area of 3/4"-10 UNC

| Property | in² | mm² |
| --- | --- | --- |
| Tensile stress area | 0.33446 | 215.78 |

The effective cross-section used to size a 3/4"-10 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 3/4"-10 UNC

A 3/4 fastener is not always 3/4"-10 UNC. These are the other standard pitches cut on the same nominal size.

| Thread | Series | Pitch | Tap drill |
| --- | --- | --- | --- |
| [3/4"-20 UNEF](https://shopmath.org/threads/unef/3-4-20.md) | Unified Extra Fine (UNEF) | 20 TPI | 45/64 |
| [3/4"-16 UNF](https://shopmath.org/threads/unf/3-4-16.md) | Unified Fine (UNF) | 16 TPI | 11/16 |

## Sources and Method for 3/4"-10 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 3/4"-10 UNC

### What is the tap drill size for 3/4"-10 UNC?

The tap drill for 3/4"-10 UNC is 21/32 — 0.6563 in (16.669 mm). That leaves 72.2% thread engagement with a cut tap.

### What is the pitch diameter of 3/4"-10 UNC?

The basic pitch diameter of 3/4"-10 UNC is 0.6850 in (17.399 mm). For a class 2B thread it runs 0.6850 in (17.399 mm) to 0.6927 in (17.595 mm).

### What is the minor diameter of 3/4"-10 UNC?

The basic minor diameter of 3/4"-10 UNC is 0.6417 in (16.299 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 3/4"-10 UNC?

3/4"-10 UNC has 10 threads per inch, a pitch of 0.1000 in (2.540 mm).

### What size clearance hole does a 3/4"-10 UNC fastener need?

close fit 49/64 (0.7795 in (19.799 mm)), normal fit 51/64 (0.8110 in (20.599 mm)), loose fit 57/64 (0.9055 in (23.000 mm)). The normal fit is the general-assembly default.

### What is the tensile stress area of 3/4"-10 UNC?

The tensile stress area of 3/4"-10 UNC is 0.33446 in² (215.78 mm²). Multiply it by the fastener material's allowable stress to get a load.

## Related pages

- Smaller in Unified Coarse (UNC): [5/8"-11 UNC](https://shopmath.org/threads/unc/5-8-11.md) — tap drill 17/32
- Larger in Unified Coarse (UNC): [7/8"-9 UNC](https://shopmath.org/threads/unc/7-8-9.md) — tap drill 49/64
- 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/3-4-10) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*