Thread Sizes & Tap Drills

Find metric, UNC, UNF and UNEF thread sizes, basic dimensions and reference tap drills. Browse by series and compare sizes.

111 size pages, grouped by thread series and sorted by nominal diameter, then pitch.

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Compare tap drill sizesThread sizes and reference cutting-tap drills Estimate a pilot holeMajor diameter minus pitch; confirm the selected tap’s guidance Understand UNC and UNFCoarse and fine pitch designations explained

Tap drill selection guides

These are basic dimensions and reference tap drills. Class-of-fit limits and inspection requirements come from the drawing and governing standard. Cutting taps and form taps need different pilot holes.

Metric coarse

Common metric coarse pitches; designation gives diameter × pitch in millimetres. Compare the Metric coarse size chart.

20 sizes · millimetres
Thread size	Major Ø (mm)	Pitch (mm)
M1.6x0.35	1.6	0.35
M2x0.4	2	0.4
M2.5x0.45	2.5	0.45
M3x0.5	3	0.5
M4x0.7	4	0.7
M5x0.8	5	0.8
M6x1	6	1
M8x1.25	8	1.25
M10x1.5	10	1.5
M12x1.75	12	1.75
M14x2	14	2
M16x2	16	2
M20x2.5	20	2.5
M24x3	24	3
M30x3.5	30	3.5
M36x4	36	4
M42x4.5	42	4.5
M48x5	48	5
M56x5.5	56	5.5
M64x6	64	6

Metric fine

Fine-pitch metric sizes. Check both diameter and pitch before matching a fastener. Compare the Metric fine size chart.

24 sizes · millimetres
Thread size	Major Ø (mm)	Pitch (mm)
M3x0.35	3	0.35
M4x0.5	4	0.5
M5x0.5	5	0.5
M6x0.75	6	0.75
M8x1	8	1
M10x1	10	1
M10x1.25	10	1.25
M12x1.25	12	1.25
M12x1.5	12	1.5
M14x1.5	14	1.5
M16x1.5	16	1.5
M18x1.5	18	1.5
M18x2	18	2
M20x1.5	20	1.5
M20x2	20	2
M22x2	22	2
M24x2	24	2
M27x2	27	2
M30x2	30	2
M33x2	33	2
M36x3	36	3
M39x3	39	3
M42x3	42	3
M48x3	48	3

UNC — Unified coarse

Inch threads, including numbered screws. The second number is threads per inch (TPI). Compare the UNC — Unified coarse size chart.

25 sizes · inches and TPI
Thread size	Major Ø (in)	TPI
#1-64	0.0730	64
#2-56	0.0860	56
#3-48	0.0990	48
#4-40	0.1120	40
#5-40	0.1250	40
#6-32	0.1380	32
#8-32	0.1640	32
#10-24	0.1900	24
#12-24	0.2160	24
1/4-20	0.2500	20
5/16-18	0.3125	18
3/8-16	0.3750	16
7/16-14	0.4375	14
1/2-13	0.5000	13
9/16-12	0.5625	12
5/8-11	0.6250	11
3/4-10	0.7500	10
7/8-9	0.8750	9
1-8	1.0000	8
1 1/8-7	1.1250	7
1 1/4-7	1.2500	7
1 3/8-6	1.3750	6
1 1/2-6	1.5000	6
1 3/4-5	1.7500	5
2-4 1/2	2.0000	4.5

UNF — Unified fine

Fine-pitch inch threads; the same nominal diameter does not make UNC and UNF interchangeable. Compare the UNF — Unified fine size chart.

24 sizes · inches and TPI
Thread size	Major Ø (in)	TPI
#0-80	0.0600	80
#1-72	0.0730	72
#2-64	0.0860	64
#3-56	0.0990	56
#4-48	0.1120	48
#5-44	0.1250	44
#6-40	0.1380	40
#8-36	0.1640	36
#10-32	0.1900	32
#12-28	0.2160	28
1/4-28	0.2500	28
5/16-24	0.3125	24
3/8-24	0.3750	24
7/16-20	0.4375	20
1/2-20	0.5000	20
9/16-18	0.5625	18
5/8-18	0.6250	18
3/4-16	0.7500	16
7/8-14	0.8750	14
1-12	1.0000	12
1 1/8-12	1.1250	12
1 1/4-12	1.2500	12
1 3/8-12	1.3750	12
1 1/2-12	1.5000	12

UNEF — Unified extra fine

Extra-fine inch threads. Match the complete designation and required thread class. Compare the UNEF — Unified extra fine size chart.

18 sizes · inches and TPI
Thread size	Major Ø (in)	TPI
1/4-32	0.2500	32
5/16-32	0.3125	32
3/8-32	0.3750	32
7/16-28	0.4375	28
1/2-28	0.5000	28
9/16-24	0.5625	24
5/8-24	0.6250	24
11/16-24	0.6875	24
3/4-20	0.7500	20
13/16-20	0.8125	20
7/8-20	0.8750	20
1-20	1.0000	20
1 1/16-18	1.0625	18
1 1/8-18	1.1250	18
1 3/16-18	1.1875	18
1 1/4-18	1.2500	18
1 3/8-18	1.3750	18
1 1/2-18	1.5000	18