MVA 02 rev 5 - December 2017
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12 TECHNICAL APPENDICES
12.1 Tightening torques for nuts and bolts
Tightening torques M of the chart 12-1 are valid under the following conditions:
Type UNI 5737 bolts with hexagonal heads, type UNI 5931 and UNI 6107 screws with cylindrical head, in
normal conditions of supply.
Tightening torques are assumed to be applied slowly with a torque wrench.
While maintaining the same pre-stressing values, tightening torques must be varied as follows in these
cases:
increased by 5% for UNI 5712 bolts with extra-wide heads
reduced by 10% for oiled galvanized bolts
reduced by 20% for oiled phosphate-treated bolts
reduced by 10% if bolts are tightened with an impact wrench.
D x pitch
mm
Sr
mm²
8.8
10.9
12.9
A2/A4-70
A2/A4-80
M
Nm
M
Nm
M
Nm
M
Nm
M
Nm
6
x
1
20,1
10,4
15,3
17,9
8,8
11,8
7
x
1
28,9
17,2
25
30
-
-
8
x
1,25
36,6
25
37
44
21,4
28,7
10
x
1,5
58
50
73
86
44
58
12
x
1,75
84,3
86
127
148
74
100
14
x
2
115
137
201
235
119
159
16
x
2
157
214
314
368
183
245
18
x
2,5
192
306
435
509
260
346
20
x
2,5
245
432
615
719
370
494
22
x
2,5
303
592
843
987
488
650
24
x
3
353
744
1060
1240
608
810
27
x
3
459
1100
1570
1840
-
-
30
x
3,5
561
1500
2130
2500
-
-
Chart 12-1 Tightening torques M for bolts with ISO metric threads
