Thread chart: metric and UNC/UNF threads, tap drill sizes

Data for metric coarse and fine threads and UNC/UNF threads: pitch, pitch diameter, minor diameter, tensile stress area and tap drill size.

Thread

Tap drill

–mm

Nominal diameter

–mm

Pitch

–mm

Threads per inch

–TPI

Pitch diameter

–mm

External minor diameter

–mm

Internal minor diameter

–mm

Tensile stress area

–mm²

How it works

The ISO metric thread (ISO 261, ISO 724) has a 60° profile; coarse pitch is the default, while fine pitch is used for thin-walled parts and fine adjustment. UNC and UNF are the coarse and fine series of the Unified thread system, specified in threads per inch (TPI).

Formula

d2 = d − 0.6495·P   d3 = d − 1.2269·P   D1 = d − 1.0825·P
As = π/4 · ((d2 + d3)/2)²
tap drill ≈ d − P

The tap drill is approximately the nominal diameter minus the pitch, which gives about 75–80% thread engagement. In hard materials or for long threads a drill 0.1–0.2 mm larger is often better. The tensile stress area is the basis for bolt strength calculations.

Chart

Thread	P mm	d2 mm	d3 mm	As mm²	Drill mm
Metric coarse (ISO 261)
M1.6	0.35	1.373	1.171	1.3	1.25
M2	0.40	1.740	1.509	2.1	1.60
M2.5	0.45	2.208	1.948	3.4	2.05
M3	0.50	2.675	2.387	5.0	2.50
M4	0.70	3.545	3.141	8.8	3.30
M5	0.80	4.480	4.019	14.2	4.20
M6	1.00	5.350	4.773	20.1	5.00
M8	1.25	7.188	6.466	36.6	6.75
M10	1.50	9.026	8.160	58.0	8.50
M12	1.75	10.863	9.853	84.3	10.25
M14	2.00	12.701	11.546	115.4	12.00
M16	2.00	14.701	13.546	156.7	14.00
M18	2.50	16.376	14.933	192.5	15.50
M20	2.50	18.376	16.933	244.8	17.50
M22	2.50	20.376	18.933	303.4	19.50
M24	3.00	22.051	20.319	352.5	21.00
M27	3.00	25.051	23.319	459.4	24.00
M30	3.50	27.727	25.706	560.6	26.50
M33	3.50	30.727	28.706	693.6	29.50
M36	4.00	33.402	31.093	816.7	32.00
M39	4.00	36.402	34.093	975.8	35.00
M42	4.50	39.077	36.479	1,120.9	37.50
M48	5.00	44.752	41.866	1,473.1	43.00
M56	5.50	52.428	49.252	2,030.0	50.50
M64	6.00	60.103	56.639	2,676.0	58.00
Metric fine
M8×1	1.00	7.350	6.773	39.2	7.00
M10×1	1.00	9.350	8.773	64.5	9.00
M10×1.25	1.25	9.188	8.466	61.2	8.75
M12×1.25	1.25	11.188	10.466	92.1	10.75
M12×1.5	1.50	11.026	10.160	88.1	10.50
M14×1.5	1.50	13.026	12.160	124.5	12.50
M16×1.5	1.50	15.026	14.160	167.2	14.50
M18×1.5	1.50	17.026	16.160	216.2	16.50
M20×1.5	1.50	19.026	18.160	271.5	18.50
M22×1.5	1.50	21.026	20.160	333.1	20.50
M24×2	2.00	22.701	21.546	384.4	22.00
M27×2	2.00	25.701	24.546	495.7	25.00
M30×2	2.00	28.701	27.546	621.2	28.00
M33×2	2.00	31.701	30.546	760.8	31.00
M36×3	3.00	34.051	32.319	864.9	33.00
M39×3	3.00	37.051	35.319	1,028.4	36.00
M42×3	3.00	40.051	38.319	1,206.0	39.00
M48×3	3.00	46.051	44.319	1,603.6	45.00
UNC
#4-40 UNC	0.635	2.432	2.066	3.9	2.21
#6-32 UNC	0.794	2.990	2.531	5.9	2.71
#8-32 UNC	0.794	3.650	3.192	9.0	3.37
#10-24 UNC	1.058	4.139	3.528	11.3	3.77
1/4-20 UNC	1.270	5.525	4.792	20.5	5.08
5/16-18 UNC	1.411	7.021	6.206	33.8	6.53
3/8-16 UNC	1.587	8.494	7.577	50.0	7.94
7/16-14 UNC	1.814	9.934	8.887	68.6	9.30
1/2-13 UNC	1.954	11.431	10.303	91.5	10.75
9/16-12 UNC	2.117	12.913	11.691	117.4	12.17
5/8-11 UNC	2.309	14.375	13.042	145.8	13.57
3/4-10 UNC	2.540	17.400	15.934	215.8	16.51
7/8-9 UNC	2.822	20.392	18.763	297.9	19.40
1-8 UNC	3.175	23.338	21.505	390.8	22.22
UNF
#4-48 UNF	0.529	2.501	2.196	4.3	2.32
#6-40 UNF	0.635	3.093	2.726	6.5	2.87
#8-36 UNF	0.706	3.707	3.300	9.5	3.46
#10-32 UNF	0.794	4.310	3.852	12.9	4.03
1/4-28 UNF	0.907	5.761	5.237	23.5	5.44
5/16-24 UNF	1.058	7.250	6.639	37.5	6.88
3/8-24 UNF	1.058	8.838	8.227	56.7	8.47
7/16-20 UNF	1.270	10.288	9.554	76.6	9.84
1/2-20 UNF	1.270	11.875	11.142	103.2	11.43
9/16-18 UNF	1.411	13.371	12.556	131.0	12.88
5/8-18 UNF	1.411	14.958	14.144	165.1	14.46
3/4-16 UNF	1.587	18.019	17.102	240.6	17.46
7/8-14 UNF	1.814	21.047	19.999	328.7	20.41
1-12 UNF	2.117	24.025	22.803	427.8	23.28

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