Standard Metric Bolt Shank Dimensions

Page Last updated 13/6/2006

All countries in the world except USA, Liberia, and Myanmar use millimeters (mm).   USA citizens:  Conversion factor is 25.400000 mm/inch.  Areas herein are accurate to five significant digits using exact converted USA diameters and pitches (not rounded USA diameters and pitches listed herein).  M and MJ are metric thread profiles.  Size designations not beginning with "M" in Table 1 are UN and UNJ thread profiles (non-metric).  Blank values in Table 1 mean nonexistent fastener size.  Dark shaded values mean typically never used and typically unavailable fastener size.

Table 1  Standard Metric and USA Bolt Shank Dimensions  (All dimensions in units of mm or mm2 unless otherwise specified.)

      Coarse Pitch Threads Fine Pitch Threads
Size Desig- nation Nominal (Major) Diam- eter,
Dn
Nominal Shank Area, An Threads per 
inch,
n
Pitch (mm per thread), p Pitch Dia- meter, dp Minor Dia- meter Area,
As
M, UNC, UNRC Tensile Stress Area,
A ts
MJ, UNJC Tensile Stress Area,
A ts
Threads per 
inch,
n
Pitch 
(mm per thread),
p
Pitch Dia- meter, dp Minor Dia- meter Area,
As
M, UNF, UNRF Tensile Stress Area,
A ts
MJ, UNJF Tensile Stress Area,
A ts
                             
0 1.5240 1.8241             80 0.31750 1.3178 0.9704 1.1588 1.3639
M1.6 1.6000 2.0106   0.35000 1.3727 1.0762 1.2700 1.4799
1 1.8542 2.7002 64 0.39688 1.5964 1.4074 1.6915 2.0016 72 0.35278 1.6251 1.5304 1.7920 2.0741
M2 2.0000 3.1416   0.40000 1.7402 1.7890 2.0732 2.3784
2 2.1844 3.7476 56 0.45357 1.8898 1.9986 2.3847 2.8049 64 0.39688 1.9266 2.1874 2.5383 2.9153
M2.5 2.5000 4.9087   0.45000 2.2077 2.9801 3.3908 3.8280
3 2.5146 4.9662 48 0.52917 2.1709 2.6222 3.1386 3.7014 56 0.45357 2.2200 2.9116 3.3741 3.8707
4 2.8448 6.3561 40 0.63500 2.4324 3.2045 3.8922 4.6467 48 0.52917 2.5011 3.6555 4.2611 4.9130
M3 3.0000 7.0686   0.50000 2.6752 4.4734 5.0308 5.6210
M3.5 3.5000 9.6211   0.60000 3.1103 5.9997 6.7752 7.5979
6 3.5052 9.6497 32 0.79375 2.9896 4.8075 5.8615 7.0199 40 0.63500 3.0928 5.6424 6.5440 7.5124
M4 4.0000 12.566   0.70000 3.5453 7.7496 8.7787 9.8720
8 4.1656 13.628 32 0.79375 3.6500 7.7166 9.0379 10.464 36 0.70556 3.7073 8.2910 9.5016 10.795
10 4.8260 18.292 24 1.0583 4.1386 9.3546 11.311 13.452 32 0.79375 4.3104 11.311 12.899 14.593
M5 5.0000 19.635   0.8000 4.4804 12.683 14.183 15.766
12 5.4864 23.641 24 1.0583 4.7990 13.277 15.590 18.088 28 0.90714 4.8972 14.576 16.638 18.836
M6 6.0000 28.274   1.0000 5.3505 17.894 20.123 22.484
0.2500 6.3500 31.669 20 1.2700 5.5251 17.351 20.530 23.976 28 0.90714 5.7608 21.006 23.467 26.065
0.3125 7.9375 49.483 18 1.4111 7.0210 29.267 33.826 38.715 24 1.0583 7.2501 33.826 37.462 41.284
M8 8.0000 50.265   1.2500 7.1881 32.841 36.609 40.581   1.0000 7.3505 36.030 39.167 42.435
0.3750 9.5250 71.256 16 1.5875 8.4939 43.741 49.994 56.663 24 1.0583 8.8376 52.170 56.663 61.342
M10 10.000 78.540   1.5000 9.0257 52.292 57.990 63.981   1.2500 9.1881 56.297 61.199 66.304
0.4375 11.112 96.987 14 1.8143 9.9341 60.210 68.586 77.508 20 1.2700 10.288 70.327 76.591 83.123
M12 12.000 113.10   1.7500 10.863 76.247 84.267 92.687   1.2500 11.188 86.037 92.072 98.311
0.5000 12.700 126.68 13 1.9538 11.431 81.103 91.548 102.63 20 1.2700 11.875 95.903 103.20 110.76
M14 14.000 153.94   2.0000 12.701 104.71 115.44 126.70   1.5000 13.026 116.13 124.55 133.26
0.5625 14.288 160.33 12 2.1167 12.913 104.55 117.38 130.96 18 1.4111 13.371 121.82 130.96 140.42
0.6250 15.875 197.93 11 2.3091 14.375 130.20 145.81 162.30 18 1.4111 14.958 154.86 165.13 175.74
M16 16.000 201.06   2.0000 14.701 144.12 156.67 169.74   1.5000 15.026 157.47 167.25 177.32
0.7500 19.050 285.02 10 2.5400 17.400 194.84 215.78 237.79 16 1.5875 18.019 226.65 240.62 255.00
M20 20.000 314.16   2.5000 18.376 225.19 244.79 265.22   1.5000 19.026 259.00 271.50 284.30
M22* 22.000 380.13   2.5000 20.376 281.53 303.40 326.09   1.5000 21.026 319.20 333.06 347.21
0.8750 22.225 387.95 9 2.8222 20.392 270.51 297.89 326.59 14 1.8143 21.047 310.03 328.69 347.90
M24 24.000 452.39   3.0000 22.051 324.27 352.50 381.91   2.0000 22.701 364.61 384.42 404.74
1.0000 25.400 506.71 8 3.1750 23.338 355.51 390.80 427.77 12 2.1167 24.025 402.94 427.77 453.34
M27* 27.000 572.56   3.0000 25.051 427.09 459.41 492.90   2.0000 25.701 473.22 495.74 518.79
1.1250 28.575 641.30 7 3.6286 26.218 447.18 492.44 539.88 12 2.1167 27.200 523.82 552.08 581.08
M30 30.000 706.86   3.5000 27.727 518.99 560.59 603.79   2.0000 28.701 595.96 621.20 646.97
1.2500 31.750 791.73 7 3.6286 29.393 574.10 625.23 678.55 12 2.1167 30.375 660.54 692.22 724.65
M33 33.000 855.30   3.5000 30.727 647.19 693.55     2.0000 31.701 732.83 760.80 789.29
1.3750 34.925 957.99 6 4.2333 32.175 680.06 745.09 813.09 12 2.1167 33.550 813.09 848.20 884.06
M36 36.000 1017.9   4.0000 33.402 759.28 816.72 876.26   2.0000 34.701 883.85 914.53 945.74
1.5000 38.100 1140.1 6 4.2333 35.350 834.73 906.62 981.47 12 2.1167 36.725 981.47 1020.0 1059.3
                             
                             
                             
                             

*  M22 x 2.5 and M27 x 3 for high strength structural steel fasteners only.

M and MJ are metric thread profiles.  Size designations not beginning with "M" in Table 1 are UN and UNJ thread profiles (non-metric), no longer used anywhere in the world except in a few behind-the-times organizations in USA.

You can look up each value in Table 1, above, or you can use the Table 2 formulas to calculate the values yourself.  In the following table, Dn is nominal shank diameter (fastener size) from Table 1.  Pitch p is fastener longitudinal length per thread.  Note that p = 1 / n, where n = threads per unit length.  Le is thread engagement length.
 

Table 2  Bolt Shank Geometric Formulas

Fastener Stress Analysis Quantity Description Sym- bol Value (for various Thread Profiles) Source
M UN, UNR MJ UNJ
Thread profile angle a 60 60 60 60 ISO 68-1, 1998, Fig. 1, p. 2.
Minor diameter Dm Dn 1.226869 p Dn 1.299038 p Same as
M profile.
Same as
UNR profile.
ISO 898-1, 1999, Sect. 8.2, p. 13;  ASME B1.1, 1989, Sect. 8.3.1.f, p. 53.
Tensile stress diameter Dts Dn 0.938194 p Dn 0.974279 p dp ISO 898-1, 1999, Sect. 8.2, p. 13;  MIL-HDBK-60, 1990, Sect. 110.1, p. 27.
Pitch diameter dp Dn 0.75 p sin a ISO 724, 1993, p. 2.
Shear stress diameter, shank in shear plane Ds Dn  
Shear stress diameter, threads in shear plane Ds Dts.  Or you can conservatively use Dm. NASA TM-106943, 1995, p. 16.
Thread shear (stripping) area, sloppy thread tolerances Ath 0.333 p dp Le Barrett, Fastener Design Manual, NASA RP-1228, 1990, p. 21.
Thread shear area, both threads class 2 or 3 (ISO class 6H/6g) thread tolerance Ath 0.5 p dp Le FED-STD-H28/2B, 1991, Table II.B.1, p. 57, Eq. 7.

Thread engagement length.  In general, according to Machine Design magazine, the minimum recommended length of engagement is 0.75 to 1 times the bolt major diameter for threading into steel and other materials of comparable hardness; and 1 to 1.5 times the bolt major diameter for threading into brass, cast iron, and aluminum.  These lengths of engagement specified are for full threads engaged, not overall bolt length.  Regarding partial threads in the chamfers on the ends of internal or external threads, FED-STD-H28/2B, 1991, Sect. 7.7.2, p. 61, specifies that approximately half the countersink or chamfer depth may be included in the length of engagement calculation.