---
type: "thread"
name: "#10-24 UNC"
designation: "#10-24 UNC"
series: "unc"
series_name: "Unified Coarse (UNC)"
system: "unified"
size_label: "#10"
tpi: 24
pitch_in: 0.041667
pitch_mm: 1.0583
basic_major_dia_in: 0.19
basic_major_dia_mm: 4.826
basic_pitch_dia_in: 0.1629
basic_pitch_dia_mm: 4.1377
basic_minor_dia_in: 0.1449
basic_minor_dia_mm: 3.6805
tap_drill: "#25"
tap_drill_dia_in: 0.1495
tap_drill_dia_mm: 3.7973
tap_drill_thread_pct: 74.8
clearance_normal_drill: "7/32"
tensile_stress_area_sqin: 0.017531
tensile_stress_area_sqmm: 11.31
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/10-24
---

# #10-24 UNC Thread — Dimensions, Tap Drill & Clearance

The tap drill for #10-24 UNC is #25 — 0.1495 in (3.797 mm) — which leaves 74.8% thread engagement with a cut tap. Basic pitch diameter is 0.1629 in (4.138 mm) and basic minor diameter is 0.1449 in (3.680 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**: #10-24 UNC
- **Threads per inch**: 24
- **Tap drill**: #25
- **Standard**: ASME B1.1 (reference values based on the ASME B1.1 system; not a compliance claim)

## Basic Thread Dimensions for #10-24 UNC

| Property | Inch | Millimetre |
| --- | --- | --- |
| Basic major diameter | 0.1900 | 4.826 |
| Threads per inch | 24 | — |
| Pitch | 0.0417 | 1.058 |
| Basic pitch diameter | 0.1629 | 4.138 |
| Basic minor diameter | 0.1449 | 3.680 |
| External thread root diameter | 0.1404 | 3.566 |
| Sharp V thread height (H) | 0.0361 | 0.917 |

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

## Tap Drill Sizes for #10-24 UNC

Cut taps, from 50% to 85% thread engagement. The shop default is 75% — a #25 drill.

| Thread % | Target hole Ø (in) | Target hole Ø (mm) | Drill | Drill Ø (in) | Drill Ø (mm) | Actual thread % |
| --- | --- | --- | --- | --- | --- | --- |
| 50% | 0.1629 | 4.138 | #20 | 0.1610 | 4.089 | 53.6 |
| 60% | 0.1575 | 4.000 | #22 | 0.1570 | 3.988 | 61.0 |
| 65% | 0.1548 | 3.932 | #23 | 0.1540 | 3.912 | 66.5 |
| 70% | 0.1521 | 3.863 | #24 | 0.1520 | 3.861 | 70.2 |
| 75% (default) | 0.1494 | 3.795 | #25 | 0.1495 | 3.797 | 74.8 |
| 80% | 0.1467 | 3.726 | #26 | 0.1470 | 3.734 | 79.4 |
| 85% | 0.1440 | 3.658 | #27 | 0.1440 | 3.658 | 85.0 |

_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 #10-24 UNC

The through-hole a #10-24 UNC fastener passes freely, not the tapped hole.

| Fit | Drill | Hole Ø (in) | Hole Ø (mm) | Use |
| --- | --- | --- | --- | --- |
| Close | #6 | 0.2047 | 5.199 | Located joints, dowelled assemblies |
| Normal | 7/32 | 0.2205 | 5.601 | General assembly — the default |
| Loose | 15/64 | 0.2362 | 5.999 | Slotted or adjustable joints, weldments |

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

## Thread Class Limits for #10-24 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 | 0.1890 | 4.801 | 0.1900 | 4.826 |
| Major Ø min | 0.1818 | 4.618 | 0.1828 | 4.643 |
| Pitch Ø max | 0.1619 | 4.112 | 0.1629 | 4.138 |
| Pitch Ø min | 0.1586 | 4.028 | 0.1604 | 4.074 |
| Pitch Ø tolerance | 0.0033 | 0.084 | 0.0025 | 0.064 |
| Minor Ø max | 0.1349 | 3.426 | 0.1359 | 3.452 |
| Minor Ø min | 0.1316 | 3.343 | 0.1334 | 3.388 |
| 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 | 0.2003 | 5.088 | 0.1993 | 5.062 |
| Major Ø min | 0.1900 | 4.826 | 0.1900 | 4.826 |
| Pitch Ø max | 0.1673 | 4.249 | 0.1662 | 4.221 |
| Pitch Ø min | 0.1629 | 4.138 | 0.1629 | 4.138 |
| Pitch Ø tolerance | 0.0043 | 0.109 | 0.0032 | 0.081 |
| Minor Ø max | 0.1555 | 3.950 | 0.1555 | 3.950 |
| Minor Ø min | 0.1449 | 3.680 | 0.1449 | 3.680 |
| Allowance | 0.0000 | 0.000 | 0.0000 | 0.000 |

## Tensile Stress Area of #10-24 UNC

| Property | in² | mm² |
| --- | --- | --- |
| Tensile stress area | 0.01753 | 11.31 |

The effective cross-section used to size a #10-24 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 #10-24 UNC

A #10 fastener is not always #10-24 UNC. These are the other standard pitches cut on the same nominal size.

| Thread | Series | Pitch | Tap drill |
| --- | --- | --- | --- |
| [#10-32 UNF](https://shopmath.org/threads/unf/10-32.md) | Unified Fine (UNF) | 32 TPI | #21 |

## Sources and Method for #10-24 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 #10-24 UNC

### What is the tap drill size for #10-24 UNC?

The tap drill for #10-24 UNC is #25 — 0.1495 in (3.797 mm). That leaves 74.8% thread engagement with a cut tap.

### What is the pitch diameter of #10-24 UNC?

The basic pitch diameter of #10-24 UNC is 0.1629 in (4.138 mm). For a class 2B thread it runs 0.1629 in (4.138 mm) to 0.1673 in (4.249 mm).

### What is the minor diameter of #10-24 UNC?

The basic minor diameter of #10-24 UNC is 0.1449 in (3.680 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 #10-24 UNC?

#10-24 UNC has 24 threads per inch, a pitch of 0.0417 in (1.058 mm).

### What size clearance hole does a #10-24 UNC fastener need?

close fit #6 (0.2047 in (5.199 mm)), normal fit 7/32 (0.2205 in (5.601 mm)), loose fit 15/64 (0.2362 in (5.999 mm)). The normal fit is the general-assembly default.

### What is the tensile stress area of #10-24 UNC?

The tensile stress area of #10-24 UNC is 0.01753 in² (11.31 mm²). Multiply it by the fastener material's allowable stress to get a load.

## Related pages

- Smaller in Unified Coarse (UNC): [#8-32 UNC](https://shopmath.org/threads/unc/8-32.md) — tap drill #29
- Larger in Unified Coarse (UNC): [#12-24 UNC](https://shopmath.org/threads/unc/12-24.md) — tap drill #16
- 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/10-24) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*