Screw Forces and Torque

Ruuvivoimat ja kiristysmomentti

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

60º                  = 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

The table shows the tensile stress, tightening force and tightening torque of the screws. The same can be calculated in a simple way as shown in the table. Here the calculation is based on the smallest known M4 screw.

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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 - 40389)
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