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
Equivalent
Imperial
bolt size (mm)
Wrench
Diameter
a (inches)
Pitch Root Area
(mm2)
Across
Flats
Across
Corners
M12 1.75 72.398 21.00 24.25 31.75 20.64 15.88 15.88 1/2 1 1/2
M16 2.00 138.324 27.00 31.18 44.45 28.58 20.64 20.64 5/8 1 3/4
M20 2.50 217.051 34.00 39.26 52.39 31.75 23.81 23.81 3/4 2 1/16
M22 2.50 272.419 36.00 41.57 53.98 33.34 25.40 25.40 7/8 2 3/8
M24 3.00 312.748 41.00 47.34 58.74 36.51 28.58 28.58 1 2 5/8
M27 3.00 413.852 46.00 53.12 63.50 38.10 29.00 29.00 1 1/8 2 7/8
M30 3.50 502.965 50.00 57.74 73.03 46.04 33.34 33.34 1 1/4 3 1/4
M36 4.00 738.015 60.00 69.28 84.14 53.97 39.69 39.69 1 1/2 3 3/4
M42 4.50 1018.218 70.00 80.83 100.00 61.91 - 49.21 1 3/4 4 1/4
M48 5.00 1342.959 80.00 92.38 112.71 68.26 - 55.56 2 4 3/4
M56 5.50 1862.725 90.00 103.92 127.00 76.20 - 63.50 2 1/4 5 1/4
M64 6.00 2467.150 100.00 115.47 139.70 84.14 - 66.68 2 1/2 5 7/8
M72 6.00 3221.775 110.00 127.02 155.58 88.90 - 69.85 2 3/4 6 1/2
M80 6.00 4076.831 120.00 138.56 166.69 93.66 - 74.61 3 1/4 7 1/4
M90 6.00 5287.085 135.00 155.88 188.91 107.95 - 84.14 3 1/2 8
M100 6.00 6651.528 150.00 173.21 207.96 119.06 - 93.66 4 9