Metric bolting - Table below provides data on root area of stud bolts, dimensions of nuts and minimum recommended dimensions for tightening the nuts.

All dimensions are in "mm" unless noted otherwise.

Bolt Dimensions
STUD BOLT ROOT AREA AND NUT DIMENSIONS
BOLT
SIZE
dB
Threads Nut Dimensions Bolt
Spacing
B
Radial
Distance
Rh
Radial
Distance
Rr
Edge
Distance
E
Wrench
Diameter
a (inch)
Pitch Minor
Diamin (mm)
Root Area
(mm2)
Root Area
(inch2)
Across
Flats
Across
Corners
M12 1.75 9.602 72.40 0.1122 21.00 24.25 31.75 20.64 15.88 15.88 1 1/2
M16 2.00 13.271 138.32 0.2144 27.00 31.18 44.45 28.58 20.64 20.64 1 3/4
M20 2.50 16.625 217.08 0.3365 34.00 39.26 52.39 31.75 23.81 23.81 2 1/16
M22 2.50 18.625 272.45 0.4223 36.00 41.57 53.98 33.34 25.40 25.40 2 3/8
M24 3.00 19.955 312.75 0.4848 41.00 47.34 58.74 36.51 28.58 28.58 2 5/8
M27 3.00 22.955 413.85 0.6415 46.00 53.12 63.50 38.10 29.00 29.00 2 7/8
M30 3.50 25.306 502.96 0.7796 50.00 57.74 73.03 46.04 33.34 33.34 3 1/4
M36 4.00 30.655 738.06 1.1440 60.00 69.28 84.14 53.97 39.69 39.69 3 3/4
M42 4.50 36.007 1018.27 1.5783 70.00 80.83 100.00 61.91 - 49.21 4 1/4
M48 5.00 41.352 1343.02 2.0817 80.00 92.38 112.71 68.26 - 55.56 4 3/4
M56 5.50 48.700 1862.72 2.8872 90.00 103.92 127.00 76.20 - 63.50 5 1/4
M64 6.00 56.048 2467.23 3.8242 100.00 115.47 139.70 84.14 - 66.68 5 7/8
M72 6.00 64.047 3221.72 4.9937 110.00 127.02 155.58 88.90 - 69.85 6 1/2
M80 6.00 72.047 4076.82 6.3191 120.00 138.56 166.69 93.66 - 74.61 7 1/4
M90 6.00 82.047 5287.07 8.1950 135.00 155.88 188.91 107.95 - 84.14 8
M100 6.00 92.027 6651.51 10.3099 150.00 173.21 207.96 119.06 - 93.66 9