Thread series · UNC

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

Name: Unified Coarse (UNC) thread dimensions and tap drill sizes
Creator: ShopMath

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

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

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

Citation

ShopMath. "Unified Coarse (UNC) Thread Chart — All Sizes, Dimensions & Tap Drills." ShopMath, verified August 1, 2026, https://shopmath.org/threads/unc

BibTeX

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

Permanent URL

https://shopmath.org/threads/unc

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