Thread series · UNEF

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

Name: Unified Extra Fine (UNEF) thread dimensions and tap drill sizes
Creator: ShopMath

https://shopmath.org/threads/unef · data verified August 1, 2026

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

25 sizes, 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.

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

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)

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

Computed from the standard's formulas, then checked against published tables.

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

How this data is built and checked →

How to Cite This UNEF Thread Chart

Citation

ShopMath. "Unified Extra Fine (UNEF) Thread Chart — All Sizes, Dimensions & Tap Drills." ShopMath, verified August 1, 2026, https://shopmath.org/threads/unef

BibTeX

@misc{shopmath-threads-unef,
  title        = {Unified Extra Fine (UNEF) Thread Chart — All Sizes, Dimensions & Tap Drills},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/threads/unef}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/threads/unef

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