 Screw Forces and Torque
Metric standard thread
640 N/mm2 = Material 0,2 -limit
0,15 µ = Friction factor of the thread
0,15 µ = Friction factor of the nut
60ŗ = Flank angle of the thread
0,4 - 0,5 - 0,63 - 0,8 - 1 - 1,25 - 1,6 - 2,0
M4 - M5 - M6 - M8 - M10 - M12 - M16 - M20
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Tensile tress Clamping force Needed tightening
max. max. torque
N / mm2 N Calculation Nm Calculation
M4 559,36 4911 Given value 2,6 Given value
M5* 562,61 7989 1,618 x 4911= 7946 5,0 21 x 2,6 = 5,2
M6** 561,22 11280 1,6182 x 4911= 12857 8,6 22 x 2,6 = 10,4
M8 563,34 20618 1,6183 x 4911= 20802 20,7 23 x 2,6 = 20,8
M10 564,52 32742 1,6184 x 4911= 33658 40,2 24 x 2,6 = 41,6
M12*** 565,26 47652 1,6185 x 4911= 54458 68,3 25 x 2,6 = 83,2
M16 568,52 89257 1,6186 x 4911= 88113 165,0 26 x 2,6 = 166,4
M20 568,52 139286 1,6187 x 4911= 142567 322,5 27 x 2,6 = 332,8
M24 568,52 200686 1,6188 x 4911= 230674 554,6 28 x 2,6 = 665,6
* Fibonacci Numbers start 1 - 1 - 2 ... Pascal's Triangle has the same form.
The second is twice the smallest 1 + 1 = 2
2.6 x 2 = 5,0 (not decimal accuracy)
** On the ratio queue, the screw size is M6.3 (0.5 - 0.6.3 - 0.8), which is not the case. This can convert to M6 screw by simplified calculation.
(6/6,3)4 x 12857 = 10577 (6/6,3)5 x10,4 = 8,2
(24/25)4 x 230674 = 195922 (24/25)5 x 665,6 = 542,7
2 x surface area = 4 2 x surface area + moment = 5
*** On the ratio queue, the screw size is M12.5 (0.8 - 1 - 1.25 - 16), which is not the case.
(12/12,5)4 x 54458 = 46254 (12/12,5)5 x 83,2 = 67,8
3.1 Example:
M16 screw clamping force according to the table is 89257 N. Wanted M16 bolt clamping force is 25 % lower, in other words 89 257 N /1.25 = 714 056 N
=> Tightening torque = 165 Nm /1.25 = 132 Nm
27.10.2011*15:20 (390 -
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