---
type: "thread-series"
series: "unef"
name: "Unified Extra Fine (UNEF)"
system: "unified"
size_count: 25
smallest: "#12-32 UNEF"
largest: "1 11/16\"-18 UNEF"
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/unef
---

# Unified Extra Fine (UNEF) Thread Chart — All 25 Sizes, Dimensions & Tap Drills

The Unified Extra Fine (UNEF) series covers 25 standard sizes, from #12-32 UNEF to 1 11/16"-18 UNEF, and 25 of them carry a tap drill recommendation. The Unified extra-fine inch thread series, used for thin-wall and adjustment threads.

- **Sizes**: 25
- **Smallest**: #12-32 UNEF
- **Largest**: 1 11/16"-18 UNEF
- **Standard**: ASME B1.1 (reference values based on the ASME B1.1 system; not a compliance claim)

## Every UNEF 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) |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| [#12-32 UNEF](https://shopmath.org/threads/unef/12-32.md) | 32 | 0.2160 | 5.486 | 0.1957 | 4.971 | 0.1822 | 4.628 | #13 | 0.1850 | 4.699 |
| [1/4"-32 UNEF](https://shopmath.org/threads/unef/1-4-32.md) | 32 | 0.2500 | 6.350 | 0.2297 | 5.834 | 0.2162 | 5.492 | 7/32 | 0.2188 | 5.556 |
| [5/16"-32 UNEF](https://shopmath.org/threads/unef/5-16-32.md) | 32 | 0.3125 | 7.938 | 0.2922 | 7.422 | 0.2787 | 7.079 | 9/32 | 0.2813 | 7.144 |
| [3/8"-32 UNEF](https://shopmath.org/threads/unef/3-8-32.md) | 32 | 0.3750 | 9.525 | 0.3547 | 9.009 | 0.3412 | 8.666 | 11/32 | 0.3438 | 8.731 |
| [7/16"-28 UNEF](https://shopmath.org/threads/unef/7-16-28.md) | 28 | 0.4375 | 11.113 | 0.4143 | 10.523 | 0.3988 | 10.130 | Y | 0.4040 | 10.262 |
| [1/2"-28 UNEF](https://shopmath.org/threads/unef/1-2-28.md) | 28 | 0.5000 | 12.700 | 0.4768 | 12.111 | 0.4613 | 11.717 | 15/32 | 0.4688 | 11.906 |
| [9/16"-24 UNEF](https://shopmath.org/threads/unef/9-16-24.md) | 24 | 0.5625 | 14.287 | 0.5354 | 13.599 | 0.5174 | 13.142 | 33/64 | 0.5156 | 13.097 |
| [5/8"-24 UNEF](https://shopmath.org/threads/unef/5-8-24.md) | 24 | 0.6250 | 15.875 | 0.5979 | 15.187 | 0.5799 | 14.729 | 37/64 | 0.5781 | 14.684 |
| [11/16"-24 UNEF](https://shopmath.org/threads/unef/11-16-24.md) | 24 | 0.6875 | 17.462 | 0.6604 | 16.774 | 0.6424 | 16.317 | 41/64 | 0.6406 | 16.272 |
| [3/4"-20 UNEF](https://shopmath.org/threads/unef/3-4-20.md) | 20 | 0.7500 | 19.050 | 0.7175 | 18.224 | 0.6959 | 17.676 | 45/64 | 0.7031 | 17.859 |
| [13/16"-20 UNEF](https://shopmath.org/threads/unef/13-16-20.md) | 20 | 0.8125 | 20.637 | 0.7800 | 19.812 | 0.7584 | 19.263 | 49/64 | 0.7656 | 19.447 |
| [7/8"-20 UNEF](https://shopmath.org/threads/unef/7-8-20.md) | 20 | 0.8750 | 22.225 | 0.8425 | 21.399 | 0.8209 | 20.851 | 53/64 | 0.8281 | 21.034 |
| [15/16"-20 UNEF](https://shopmath.org/threads/unef/15-16-20.md) | 20 | 0.9375 | 23.813 | 0.9050 | 22.987 | 0.8834 | 22.438 | 57/64 | 0.8906 | 22.622 |
| [1"-20 UNEF](https://shopmath.org/threads/unef/1-20.md) | 20 | 1.0000 | 25.400 | 0.9675 | 24.575 | 0.9459 | 24.026 | 61/64 | 0.9531 | 24.209 |
| [1 1/16"-18 UNEF](https://shopmath.org/threads/unef/1-1-16-18.md) | 18 | 1.0625 | 26.988 | 1.0264 | 26.071 | 1.0024 | 25.461 | 1 | 1.0000 | 25.400 |
| [1 1/8"-18 UNEF](https://shopmath.org/threads/unef/1-1-8-18.md) | 18 | 1.1250 | 28.575 | 1.0889 | 27.658 | 1.0649 | 27.049 | 1 | 1.0000 | 25.400 |
| [1 3/16"-18 UNEF](https://shopmath.org/threads/unef/1-3-16-18.md) | 18 | 1.1875 | 30.163 | 1.1514 | 29.246 | 1.1274 | 28.636 | 1 | 1.0000 | 25.400 |
| [1 1/4"-18 UNEF](https://shopmath.org/threads/unef/1-1-4-18.md) | 18 | 1.2500 | 31.750 | 1.2139 | 30.833 | 1.1899 | 30.224 | 1 | 1.0000 | 25.400 |
| [1 5/16"-18 UNEF](https://shopmath.org/threads/unef/1-5-16-18.md) | 18 | 1.3125 | 33.337 | 1.2764 | 32.421 | 1.2524 | 31.811 | 1 | 1.0000 | 25.400 |
| [1 3/8"-18 UNEF](https://shopmath.org/threads/unef/1-3-8-18.md) | 18 | 1.3750 | 34.925 | 1.3389 | 34.008 | 1.3149 | 33.398 | 1 | 1.0000 | 25.400 |
| [1 7/16"-18 UNEF](https://shopmath.org/threads/unef/1-7-16-18.md) | 18 | 1.4375 | 36.513 | 1.4014 | 35.596 | 1.3774 | 34.986 | 1 | 1.0000 | 25.400 |
| [1 1/2"-18 UNEF](https://shopmath.org/threads/unef/1-1-2-18.md) | 18 | 1.5000 | 38.100 | 1.4639 | 37.183 | 1.4399 | 36.574 | 1 | 1.0000 | 25.400 |
| [1 9/16"-18 UNEF](https://shopmath.org/threads/unef/1-9-16-18.md) | 18 | 1.5625 | 39.688 | 1.5264 | 38.771 | 1.5024 | 38.161 | 1 | 1.0000 | 25.400 |
| [1 5/8"-18 UNEF](https://shopmath.org/threads/unef/1-5-8-18.md) | 18 | 1.6250 | 41.275 | 1.5889 | 40.358 | 1.5649 | 39.748 | 1 | 1.0000 | 25.400 |
| [1 11/16"-18 UNEF](https://shopmath.org/threads/unef/1-11-16-18.md) | 18 | 1.6875 | 42.862 | 1.6514 | 41.946 | 1.6274 | 41.336 | 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 UNEF Thread Chart

### UNEF 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/unef) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*