---
type: "thread-series"
series: "unc"
name: "Unified Coarse (UNC)"
system: "unified"
size_count: 33
smallest: "#1-64 UNC"
largest: "4\"-4 UNC"
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
---

# Unified Coarse (UNC) Thread Chart — All 33 Sizes, Dimensions & Tap Drills

The Unified Coarse (UNC) series covers 33 standard sizes, from #1-64 UNC to 4"-4 UNC, and 33 of them carry a tap drill recommendation. The Unified coarse inch thread series — the default inch thread for general assembly.

- **Sizes**: 33
- **Smallest**: #1-64 UNC
- **Largest**: 4"-4 UNC
- **Standard**: ASME B1.1 (reference values based on the ASME B1.1 system; not a compliance claim)

## Every UNC Thread Size — Dimensions and Tap Drills

Ordered smallest to largest. Every row links to the full page for that thread, with class limits, clearance holes and tap drills across 50–85% engagement.

| Thread | TPI | Major Ø (in) | Major Ø (mm) | Pitch Ø (in) | Pitch Ø (mm) | Minor Ø (in) | Minor Ø (mm) | Tap drill | Tap drill Ø (in) | Tap drill Ø (mm) |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| [#1-64 UNC](https://shopmath.org/threads/unc/1-64.md) | 64 | 0.0730 | 1.854 | 0.0629 | 1.598 | 0.0561 | 1.425 | #53 | 0.0595 | 1.511 |
| [#2-56 UNC](https://shopmath.org/threads/unc/2-56.md) | 56 | 0.0860 | 2.184 | 0.0744 | 1.890 | 0.0667 | 1.694 | #50 | 0.0700 | 1.778 |
| [#3-48 UNC](https://shopmath.org/threads/unc/3-48.md) | 48 | 0.0990 | 2.515 | 0.0855 | 2.172 | 0.0764 | 1.941 | #47 | 0.0785 | 1.994 |
| [#4-40 UNC](https://shopmath.org/threads/unc/4-40.md) | 40 | 0.1120 | 2.845 | 0.0958 | 2.433 | 0.0849 | 2.156 | #43 | 0.0890 | 2.261 |
| [#5-40 UNC](https://shopmath.org/threads/unc/5-40.md) | 40 | 0.1250 | 3.175 | 0.1088 | 2.764 | 0.0979 | 2.487 | #38 | 0.1015 | 2.578 |
| [#6-32 UNC](https://shopmath.org/threads/unc/6-32.md) | 32 | 0.1380 | 3.505 | 0.1177 | 2.990 | 0.1042 | 2.647 | #36 | 0.1065 | 2.705 |
| [#8-32 UNC](https://shopmath.org/threads/unc/8-32.md) | 32 | 0.1640 | 4.166 | 0.1437 | 3.650 | 0.1302 | 3.307 | #29 | 0.1360 | 3.454 |
| [#10-24 UNC](https://shopmath.org/threads/unc/10-24.md) | 24 | 0.1900 | 4.826 | 0.1629 | 4.138 | 0.1449 | 3.680 | #25 | 0.1495 | 3.797 |
| [#12-24 UNC](https://shopmath.org/threads/unc/12-24.md) | 24 | 0.2160 | 5.486 | 0.1889 | 4.798 | 0.1709 | 4.341 | #16 | 0.1770 | 4.496 |
| [1/4"-20 UNC](https://shopmath.org/threads/unc/1-4-20.md) | 20 | 0.2500 | 6.350 | 0.2175 | 5.524 | 0.1959 | 4.976 | #7 | 0.2010 | 5.105 |
| [5/16"-18 UNC](https://shopmath.org/threads/unc/5-16-18.md) | 18 | 0.3125 | 7.938 | 0.2764 | 7.021 | 0.2524 | 6.411 | F | 0.2570 | 6.528 |
| [3/8"-16 UNC](https://shopmath.org/threads/unc/3-8-16.md) | 16 | 0.3750 | 9.525 | 0.3344 | 8.494 | 0.3073 | 7.805 | 5/16 | 0.3125 | 7.938 |
| [7/16"-14 UNC](https://shopmath.org/threads/unc/7-16-14.md) | 14 | 0.4375 | 11.113 | 0.3911 | 9.934 | 0.3602 | 9.149 | U | 0.3680 | 9.347 |
| [1/2"-13 UNC](https://shopmath.org/threads/unc/1-2-13.md) | 13 | 0.5000 | 12.700 | 0.4500 | 11.430 | 0.4167 | 10.584 | 27/64 | 0.4219 | 10.716 |
| [9/16"-12 UNC](https://shopmath.org/threads/unc/9-16-12.md) | 12 | 0.5625 | 14.287 | 0.5084 | 12.913 | 0.4723 | 11.996 | 31/64 | 0.4844 | 12.303 |
| [5/8"-11 UNC](https://shopmath.org/threads/unc/5-8-11.md) | 11 | 0.6250 | 15.875 | 0.5660 | 14.376 | 0.5266 | 13.376 | 17/32 | 0.5313 | 13.494 |
| [3/4"-10 UNC](https://shopmath.org/threads/unc/3-4-10.md) | 10 | 0.7500 | 19.050 | 0.6850 | 17.399 | 0.6417 | 16.299 | 21/32 | 0.6563 | 16.669 |
| [7/8"-9 UNC](https://shopmath.org/threads/unc/7-8-9.md) | 9 | 0.8750 | 22.225 | 0.8028 | 20.391 | 0.7547 | 19.169 | 49/64 | 0.7656 | 19.447 |
| [1"-8 UNC](https://shopmath.org/threads/unc/1-8.md) | 8 | 1.0000 | 25.400 | 0.9188 | 23.337 | 0.8647 | 21.963 | 7/8 | 0.8750 | 22.225 |
| [1 1/8"-7 UNC](https://shopmath.org/threads/unc/1-1-8-7.md) | 7 | 1.1250 | 28.575 | 1.0322 | 26.218 | 0.9704 | 24.648 | 63/64 | 0.9844 | 25.003 |
| [1 1/4"-7 UNC](https://shopmath.org/threads/unc/1-1-4-7.md) | 7 | 1.2500 | 31.750 | 1.1572 | 29.393 | 1.0954 | 27.823 | 1 | 1.0000 | 25.400 |
| [1 3/8"-6 UNC](https://shopmath.org/threads/unc/1-3-8-6.md) | 6 | 1.3750 | 34.925 | 1.2667 | 32.174 | 1.1946 | 30.343 | 1 | 1.0000 | 25.400 |
| [1 1/2"-6 UNC](https://shopmath.org/threads/unc/1-1-2-6.md) | 6 | 1.5000 | 38.100 | 1.3917 | 35.349 | 1.3196 | 33.518 | 1 | 1.0000 | 25.400 |
| [1 3/4"-5 UNC](https://shopmath.org/threads/unc/1-3-4-5.md) | 5 | 1.7500 | 44.450 | 1.6201 | 41.151 | 1.5335 | 38.951 | 1 | 1.0000 | 25.400 |
| [2"-4 UNC](https://shopmath.org/threads/unc/2-4.md) | 4 | 2.0000 | 50.800 | 1.8376 | 46.675 | 1.7294 | 43.927 | 1 | 1.0000 | 25.400 |
| [2 1/4"-4 UNC](https://shopmath.org/threads/unc/2-1-4-4.md) | 4 | 2.2500 | 57.150 | 2.0876 | 53.025 | 1.9794 | 50.277 | 1 | 1.0000 | 25.400 |
| [2 1/2"-4 UNC](https://shopmath.org/threads/unc/2-1-2-4.md) | 4 | 2.5000 | 63.500 | 2.3376 | 59.375 | 2.2294 | 56.627 | 1 | 1.0000 | 25.400 |
| [2 3/4"-4 UNC](https://shopmath.org/threads/unc/2-3-4-4.md) | 4 | 2.7500 | 69.850 | 2.5876 | 65.725 | 2.4794 | 62.977 | 1 | 1.0000 | 25.400 |
| [3"-4 UNC](https://shopmath.org/threads/unc/3-4.md) | 4 | 3.0000 | 76.200 | 2.8376 | 72.075 | 2.7294 | 69.327 | 1 | 1.0000 | 25.400 |
| [3 1/4"-4 UNC](https://shopmath.org/threads/unc/3-1-4-4.md) | 4 | 3.2500 | 82.550 | 3.0876 | 78.425 | 2.9794 | 75.677 | 1 | 1.0000 | 25.400 |
| [3 1/2"-4 UNC](https://shopmath.org/threads/unc/3-1-2-4.md) | 4 | 3.5000 | 88.900 | 3.3376 | 84.775 | 3.2294 | 82.027 | 1 | 1.0000 | 25.400 |
| [3 3/4"-4 UNC](https://shopmath.org/threads/unc/3-3-4-4.md) | 4 | 3.7500 | 95.250 | 3.5876 | 91.125 | 3.4794 | 88.377 | 1 | 1.0000 | 25.400 |
| [4"-4 UNC](https://shopmath.org/threads/unc/4-4.md) | 4 | 4.0000 | 101.600 | 3.8376 | 97.475 | 3.7294 | 94.727 | 1 | 1.0000 | 25.400 |

_Basic dimensions are the theoretical values before a tolerance class is applied. Tap drills are for cut taps at the default engagement; per-size pages carry 50–85%._

## Sources and Method for the UNC Thread Chart

### UNC thread 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

### Assumptions

- Tap drill figures are for cut taps at the default thread engagement; each size page carries the full 50–85% range.
- 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

## Related pages

- Every thread series: [Screw thread reference](https://shopmath.org/threads.md)
- Cross-series chart: [Tap drill chart](https://shopmath.org/charts/tap-drill.md)
- Drill index: [Drill size chart](https://shopmath.org/charts/drill-sizes.md)

---

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