---
type: "thread"
name: "5/8\"-11 UNC"
designation: "5/8-11 UNC"
series: "unc"
series_name: "Unified Coarse (UNC)"
system: "unified"
size_label: "5/8"
tpi: 11
pitch_in: 0.090909
pitch_mm: 2.3091
basic_major_dia_in: 0.625
basic_major_dia_mm: 15.875
basic_pitch_dia_in: 0.566
basic_pitch_dia_mm: 14.3764
basic_minor_dia_in: 0.5266
basic_minor_dia_mm: 13.3756
tap_drill: "17/32"
tap_drill_dia_in: 0.53125
tap_drill_dia_mm: 13.4938
tap_drill_thread_pct: 79.4
clearance_normal_drill: "11/16"
tensile_stress_area_sqin: 0.226002
tensile_stress_area_sqmm: 145.807
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/5-8-11
---

# 5/8"-11 UNC Thread — Dimensions, Tap Drill & Clearance

The tap drill for 5/8"-11 UNC is 17/32 — 0.5313 in (13.494 mm) — which leaves 79.4% thread engagement with a cut tap. Basic pitch diameter is 0.5660 in (14.376 mm) and basic minor diameter is 0.5266 in (13.376 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**: 5/8-11 UNC
- **Threads per inch**: 11
- **Tap drill**: 17/32
- **Standard**: ASME B1.1 (reference values based on the ASME B1.1 system; not a compliance claim)

## Basic Thread Dimensions for 5/8"-11 UNC

| Property | Inch | Millimetre |
| --- | --- | --- |
| Basic major diameter | 0.6250 | 15.875 |
| Threads per inch | 11 | — |
| Pitch | 0.0909 | 2.309 |
| Basic pitch diameter | 0.5660 | 14.376 |
| Basic minor diameter | 0.5266 | 13.376 |
| External thread root diameter | 0.5167 | 13.124 |
| Sharp V thread height (H) | 0.0787 | 1.999 |

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

## Tap Drill Sizes for 5/8"-11 UNC

Cut taps, from 50% to 85% thread engagement. The shop default is 75% — a 17/32 drill.

| Thread % | Target hole Ø (in) | Target hole Ø (mm) | Drill | Drill Ø (in) | Drill Ø (mm) | Actual thread % |
| --- | --- | --- | --- | --- | --- | --- |
| 50% | 0.5660 | 14.376 | 9/16 | 0.5625 | 14.287 | 52.9 |
| 60% | 0.5541 | 14.074 | 35/64 | 0.5469 | 13.891 | 66.2 |
| 65% | 0.5482 | 13.924 | 35/64 | 0.5469 | 13.891 | 66.2 |
| 70% | 0.5423 | 13.774 | 35/64 | 0.5469 | 13.891 | 66.2 |
| 75% (default) | 0.5364 | 13.625 | 17/32 | 0.5313 | 13.494 | 79.4 |
| 80% | 0.5305 | 13.475 | 17/32 | 0.5313 | 13.494 | 79.4 |
| 85% | 0.5246 | 13.325 | 17/32 | 0.5313 | 13.494 | 79.4 |

_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 5/8"-11 UNC

The through-hole a 5/8"-11 UNC fastener passes freely, not the tapped hole.

| Fit | Drill | Hole Ø (in) | Hole Ø (mm) | Use |
| --- | --- | --- | --- | --- |
| Close | 21/32 | 0.6575 | 16.701 | Located joints, dowelled assemblies |
| Normal | 11/16 | 0.6890 | 17.501 | General assembly — the default |
| Loose | 23/32 | 0.7323 | 18.600 | Slotted or adjustable joints, weldments |

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

## Thread Class Limits for 5/8"-11 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 | 0.6233 | 15.832 | 0.6250 | 15.875 |
| Major Ø min | 0.6112 | 15.524 | 0.6129 | 15.568 |
| Pitch Ø max | 0.5643 | 14.333 | 0.5660 | 14.376 |
| Pitch Ø min | 0.5588 | 14.194 | 0.5618 | 14.270 |
| Pitch Ø tolerance | 0.0055 | 0.140 | 0.0041 | 0.104 |
| Minor Ø max | 0.5053 | 12.835 | 0.5069 | 12.875 |
| Minor Ø min | 0.4998 | 12.695 | 0.5028 | 12.771 |
| Allowance | 0.0017 | 0.043 | 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 | 0.6453 | 16.391 | 0.6435 | 16.345 |
| Major Ø min | 0.6250 | 15.875 | 0.6250 | 15.875 |
| Pitch Ø max | 0.5731 | 14.557 | 0.5713 | 14.511 |
| Pitch Ø min | 0.5660 | 14.376 | 0.5660 | 14.376 |
| Pitch Ø tolerance | 0.0072 | 0.183 | 0.0054 | 0.137 |
| Minor Ø max | 0.5460 | 13.868 | 0.5391 | 13.693 |
| Minor Ø min | 0.5266 | 13.376 | 0.5266 | 13.376 |
| Allowance | 0.0000 | 0.000 | 0.0000 | 0.000 |

## Tensile Stress Area of 5/8"-11 UNC

| Property | in² | mm² |
| --- | --- | --- |
| Tensile stress area | 0.22600 | 145.81 |

The effective cross-section used to size a 5/8"-11 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 5/8"-11 UNC

A 5/8 fastener is not always 5/8"-11 UNC. These are the other standard pitches cut on the same nominal size.

| Thread | Series | Pitch | Tap drill |
| --- | --- | --- | --- |
| [5/8"-24 UNEF](https://shopmath.org/threads/unef/5-8-24.md) | Unified Extra Fine (UNEF) | 24 TPI | 37/64 |
| [5/8"-18 UNF](https://shopmath.org/threads/unf/5-8-18.md) | Unified Fine (UNF) | 18 TPI | 37/64 |

## Sources and Method for 5/8"-11 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 5/8"-11 UNC

### What is the tap drill size for 5/8"-11 UNC?

The tap drill for 5/8"-11 UNC is 17/32 — 0.5313 in (13.494 mm). That leaves 79.4% thread engagement with a cut tap.

### What is the pitch diameter of 5/8"-11 UNC?

The basic pitch diameter of 5/8"-11 UNC is 0.5660 in (14.376 mm). For a class 2B thread it runs 0.5660 in (14.376 mm) to 0.5731 in (14.557 mm).

### What is the minor diameter of 5/8"-11 UNC?

The basic minor diameter of 5/8"-11 UNC is 0.5266 in (13.376 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 5/8"-11 UNC?

5/8"-11 UNC has 11 threads per inch, a pitch of 0.0909 in (2.309 mm).

### What size clearance hole does a 5/8"-11 UNC fastener need?

close fit 21/32 (0.6575 in (16.701 mm)), normal fit 11/16 (0.6890 in (17.501 mm)), loose fit 23/32 (0.7323 in (18.600 mm)). The normal fit is the general-assembly default.

### What is the tensile stress area of 5/8"-11 UNC?

The tensile stress area of 5/8"-11 UNC is 0.22600 in² (145.81 mm²). Multiply it by the fastener material's allowable stress to get a load.

## Related pages

- Smaller in Unified Coarse (UNC): [9/16"-12 UNC](https://shopmath.org/threads/unc/9-16-12.md) — tap drill 31/64
- Larger in Unified Coarse (UNC): [3/4"-10 UNC](https://shopmath.org/threads/unc/3-4-10.md) — tap drill 21/32
- 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/5-8-11) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*