Fasteners

Thread Size Chart

The geometry behind the designation. Every value is derived from the basic 60° thread form, so you can check any row against the formulas rather than trusting the print.

Tensile stress area is what actually carries load — not the major diameter. A 1/2-13 has a 0.500″ major diameter but only 0.1419 in² of stress area, about 72% of the solid-rod area you might assume.

Thread geometry for UNC, UNF and metric: pitch, pitch diameter, minor diameter and tensile stress area

#1-64	UNC	0.0730 in / mm	0.01562 in / mm	0.0629 in / mm	0.0561 in / mm	0.00262
#2-56	UNC	0.0860 in / mm	0.01786 in / mm	0.0744 in / mm	0.0667 in / mm	0.00370
#3-48	UNC	0.0990 in / mm	0.02083 in / mm	0.0855 in / mm	0.0765 in / mm	0.00486
#4-40	UNC	0.1120 in / mm	0.02500 in / mm	0.0958 in / mm	0.0849 in / mm	0.00603
#5-40	UNC	0.1250 in / mm	0.02500 in / mm	0.1088 in / mm	0.0979 in / mm	0.00796
#6-32	UNC	0.1380 in / mm	0.03125 in / mm	0.1177 in / mm	0.1042 in / mm	0.00909
#8-32	UNC	0.1640 in / mm	0.03125 in / mm	0.1437 in / mm	0.1302 in / mm	0.01401
#10-24	UNC	0.1900 in / mm	0.04167 in / mm	0.1629 in / mm	0.1449 in / mm	0.01753
#12-24	UNC	0.2160 in / mm	0.04167 in / mm	0.1889 in / mm	0.1709 in / mm	0.02416
1/4-20	UNC	0.2500 in / mm	0.05000 in / mm	0.2175 in / mm	0.1959 in / mm	0.03182
5/16-18	UNC	0.3125 in / mm	0.05556 in / mm	0.2764 in / mm	0.2524 in / mm	0.05243
3/8-16	UNC	0.3750 in / mm	0.06250 in / mm	0.3344 in / mm	0.3073 in / mm	0.07749
7/16-14	UNC	0.4375 in / mm	0.07143 in / mm	0.3911 in / mm	0.3602 in / mm	0.10631
1/2-13	UNC	0.5000 in / mm	0.07692 in / mm	0.4500 in / mm	0.4167 in / mm	0.14190
9/16-12	UNC	0.5625 in / mm	0.08333 in / mm	0.5084 in / mm	0.4723 in / mm	0.18194
5/8-11	UNC	0.6250 in / mm	0.09091 in / mm	0.5659 in / mm	0.5266 in / mm	0.22600
3/4-10	UNC	0.7500 in / mm	0.10000 in / mm	0.6851 in / mm	0.6418 in / mm	0.33446
7/8-9	UNC	0.8750 in / mm	0.11111 in / mm	0.8028 in / mm	0.7547 in / mm	0.46173
1-8	UNC	1.0000 in / mm	0.12500 in / mm	0.9188 in / mm	0.8647 in / mm	0.60575
1-1/8-7	UNC	1.1250 in / mm	0.14286 in / mm	1.0322 in / mm	0.9704 in / mm	0.76328
1-1/4-7	UNC	1.2500 in / mm	0.14286 in / mm	1.1572 in / mm	1.0954 in / mm	0.96911
1-3/8-6	UNC	1.3750 in / mm	0.16667 in / mm	1.2668 in / mm	1.1946 in / mm	1.15488
1-1/2-6	UNC	1.5000 in / mm	0.16667 in / mm	1.3918 in / mm	1.3196 in / mm	1.40525
#0-80	UNF	0.0600 in / mm	0.01250 in / mm	0.0519 in / mm	0.0465 in / mm	0.00180
#1-72	UNF	0.0730 in / mm	0.01389 in / mm	0.0640 in / mm	0.0580 in / mm	0.00278
#2-64	UNF	0.0860 in / mm	0.01562 in / mm	0.0759 in / mm	0.0691 in / mm	0.00393
#3-56	UNF	0.0990 in / mm	0.01786 in / mm	0.0874 in / mm	0.0797 in / mm	0.00523
#4-48	UNF	0.1120 in / mm	0.02083 in / mm	0.0985 in / mm	0.0895 in / mm	0.00660
#5-44	UNF	0.1250 in / mm	0.02273 in / mm	0.1102 in / mm	0.1004 in / mm	0.00831
#6-40	UNF	0.1380 in / mm	0.02500 in / mm	0.1218 in / mm	0.1109 in / mm	0.01014
#8-36	UNF	0.1640 in / mm	0.02778 in / mm	0.1460 in / mm	0.1339 in / mm	0.01473
#10-32	UNF	0.1900 in / mm	0.03125 in / mm	0.1697 in / mm	0.1562 in / mm	0.01999
#12-28	UNF	0.2160 in / mm	0.03571 in / mm	0.1928 in / mm	0.1773 in / mm	0.02579
1/4-28	UNF	0.2500 in / mm	0.03571 in / mm	0.2268 in / mm	0.2113 in / mm	0.03637
5/16-24	UNF	0.3125 in / mm	0.04167 in / mm	0.2854 in / mm	0.2674 in / mm	0.05807
3/8-24	UNF	0.3750 in / mm	0.04167 in / mm	0.3479 in / mm	0.3299 in / mm	0.08783
7/16-20	UNF	0.4375 in / mm	0.05000 in / mm	0.4050 in / mm	0.3834 in / mm	0.11872
1/2-20	UNF	0.5000 in / mm	0.05000 in / mm	0.4675 in / mm	0.4459 in / mm	0.15995
9/16-18	UNF	0.5625 in / mm	0.05556 in / mm	0.5264 in / mm	0.5024 in / mm	0.20298
5/8-18	UNF	0.6250 in / mm	0.05556 in / mm	0.5889 in / mm	0.5649 in / mm	0.25596
3/4-16	UNF	0.7500 in / mm	0.06250 in / mm	0.7094 in / mm	0.6823 in / mm	0.37296
7/8-14	UNF	0.8750 in / mm	0.07143 in / mm	0.8286 in / mm	0.7977 in / mm	0.50947
1-12	UNF	1.0000 in / mm	0.08333 in / mm	0.9459 in / mm	0.9098 in / mm	0.66304
1-1/8-12	UNF	1.1250 in / mm	0.08333 in / mm	1.0709 in / mm	1.0348 in / mm	0.85572
1-1/4-12	UNF	1.2500 in / mm	0.08333 in / mm	1.1959 in / mm	1.1598 in / mm	1.07295
1-3/8-12	UNF	1.3750 in / mm	0.08333 in / mm	1.3209 in / mm	1.2848 in / mm	1.31471
1-1/2-12	UNF	1.5000 in / mm	0.08333 in / mm	1.4459 in / mm	1.4098 in / mm	1.58102
M1.6×0.35	Metric Coarse	0.0630 in / mm	0.01378 in / mm	0.0540 in / mm	0.0481 in / mm	0.00197
M2×0.4	Metric Coarse	0.0787 in / mm	0.01575 in / mm	0.0685 in / mm	0.0617 in / mm	0.00321
M2.5×0.45	Metric Coarse	0.0984 in / mm	0.01772 in / mm	0.0869 in / mm	0.0792 in / mm	0.00526
M3×0.5	Metric Coarse	0.1181 in / mm	0.01969 in / mm	0.1053 in / mm	0.0968 in / mm	0.00780
M3.5×0.6	Metric Coarse	0.1378 in / mm	0.02362 in / mm	0.1225 in / mm	0.1122 in / mm	0.01050
M4×0.7	Metric Coarse	0.1575 in / mm	0.02756 in / mm	0.1396 in / mm	0.1276 in / mm	0.01361
M5×0.8	Metric Coarse	0.1969 in / mm	0.03150 in / mm	0.1764 in / mm	0.1628 in / mm	0.02198
M6×1	Metric Coarse	0.2362 in / mm	0.03937 in / mm	0.2106 in / mm	0.1936 in / mm	0.03119
M8×1.25	Metric Coarse	0.3150 in / mm	0.04921 in / mm	0.2830 in / mm	0.2617 in / mm	0.05674
M10×1.5	Metric Coarse	0.3937 in / mm	0.05906 in / mm	0.3553 in / mm	0.3298 in / mm	0.08988
M12×1.75	Metric Coarse	0.4724 in / mm	0.06890 in / mm	0.4277 in / mm	0.3979 in / mm	0.13061
M14×2	Metric Coarse	0.5512 in / mm	0.07874 in / mm	0.5000 in / mm	0.4659 in / mm	0.17893
M16×2	Metric Coarse	0.6299 in / mm	0.07874 in / mm	0.5788 in / mm	0.5447 in / mm	0.24284
M18×2.5	Metric Coarse	0.7087 in / mm	0.09843 in / mm	0.6447 in / mm	0.6021 in / mm	0.29833
M20×2.5	Metric Coarse	0.7874 in / mm	0.09843 in / mm	0.7235 in / mm	0.6809 in / mm	0.37943
M22×2.5	Metric Coarse	0.8661 in / mm	0.09843 in / mm	0.8022 in / mm	0.7596 in / mm	0.47027
M24×3	Metric Coarse	0.9449 in / mm	0.11811 in / mm	0.8682 in / mm	0.8170 in / mm	0.54638
M27×3	Metric Coarse	1.0630 in / mm	0.11811 in / mm	0.9863 in / mm	0.9351 in / mm	0.71208
M30×3.5	Metric Coarse	1.1811 in / mm	0.13780 in / mm	1.0916 in / mm	1.0319 in / mm	0.86891
M8×1	Metric Fine	0.3150 in / mm	0.03937 in / mm	0.2894 in / mm	0.2723 in / mm	0.06071
M10×1.25	Metric Fine	0.3937 in / mm	0.04921 in / mm	0.3617 in / mm	0.3404 in / mm	0.09486
M10×1	Metric Fine	0.3937 in / mm	0.03937 in / mm	0.3681 in / mm	0.3511 in / mm	0.09997
M12×1.5	Metric Fine	0.4724 in / mm	0.05906 in / mm	0.4341 in / mm	0.4085 in / mm	0.13660
M12×1.25	Metric Fine	0.4724 in / mm	0.04921 in / mm	0.4405 in / mm	0.4192 in / mm	0.14271
M14×1.5	Metric Fine	0.5512 in / mm	0.05906 in / mm	0.5128 in / mm	0.4873 in / mm	0.19305
M16×1.5	Metric Fine	0.6299 in / mm	0.05906 in / mm	0.5916 in / mm	0.5660 in / mm	0.25923
M18×1.5	Metric Fine	0.7087 in / mm	0.05906 in / mm	0.6703 in / mm	0.6447 in / mm	0.33516
M20×1.5	Metric Fine	0.7874 in / mm	0.05906 in / mm	0.7490 in / mm	0.7235 in / mm	0.42083
M22×1.5	Metric Fine	0.8661 in / mm	0.05906 in / mm	0.8278 in / mm	0.8022 in / mm	0.51624
M24×2	Metric Fine	0.9449 in / mm	0.07874 in / mm	0.8937 in / mm	0.8596 in / mm	0.59585
M27×2	Metric Fine	1.0630 in / mm	0.07874 in / mm	1.0118 in / mm	0.9778 in / mm	0.76840
M30×2	Metric Fine	1.1811 in / mm	0.07874 in / mm	1.1300 in / mm	1.0959 in / mm	0.96287

79 threads · 47 inch, 32 metric

The formulas

H  = 0.866025 × P          theoretical triangle height
d2 = D − 0.649519 × P      pitch diameter
D1 = D − 1.082532 × P      minor diameter (internal)
At = 0.7854 × (D − 0.9743/n)²      tensile stress area, inch [ASME B1.1]
As = 0.7854 × (D − 0.9382 × P)²    tensile stress area, metric [ISO 898-1]

Why tensile area, not major diameter

A threaded rod fails through the thread roots, so its load-bearing section is smaller than the nominal size suggests. Across common sizes the stress area is only 65–77% of the solid-rod area — so sizing a joint off the major diameter overstates capacity by 30% on a 1″-8 and by 54% on a 1/4-20. The smaller the fastener, the bigger the error.

Take the table with you — CSV · JSON

Data source and method

Standards: ASME B1.1 (Unified inch screw threads); ISO 68-1 / 261 / 965 (metric). Nominal diameters and pitches are factual values.
Calculation: All geometry derived from the basic 60° form using the equations above. No published table reproduced.
Verification: Tensile areas checked against 12 published values (1/4-20, 3/8-16, 1/2-13, 5/8-11, 3/4-10, 1-8, M6, M8, M10, M12, M16, M20). Maximum deviation 0.21%.

Related charts

Tap drill size chart — hole sizes for cutting these threads