--- 9 ---
400
640
994
1370
1940
2640
1090
1735
2700
3720
5280
7180
•
Diameter and effective sectional areas of bolts
6-3. Appropriate Tightening Torque for Bolts
Generally speaking, the appropriate tightening torque for a bolt can be determined by the strength grade of the
bolt and the material tightened. Tables 2, 3 and 4 below list data relative to the strength grade of various bolts and
the appropriate tightening torque. For further reference, appropriate tightening torque is calculated with the
following formula. Study and use this formula for accurate selection of tightening torque.
T = k
•
d
•
p
T: Appropriate tightening torque (kgf.cm)
d: Nominal diameter for the bolt (cm)
p: Recommended axial tightening force to be applied to the bolt (kg)
p = Rated axial stress (kg
.
mm
2
) x 0.8 x Effective sectional area of the bolt (mm
2
)
k: Torque coefficient (0.17)
Strength grade
Rated axial stress (kgf
.
mm
2
)
Material
Heat treatment
4.8
8.8
10.9
12.9
29.1
58.2
79.2
95
Carbon steel such as SS and SC
Special alloy steel such as SNC, SCM and SNCM
Not treated
Treated .... Hard material
Nominal diameter of bolt
Effective sectional area
of bolt (mm
2
)
M12 x 1.75
84.3
M14 x 2.0
115.0
M16 x 2.0
157.0
M18 x 2.5
192.0
M20 x 2.5
245.0
M22 x 2.5
303.0
•
Tightening torque according to strength grade of bolts
<Table 2>
•
Strength grade and rated axial stress of bolts
<Table 3>
Nominal
diameter of bolt
Strength grade
M12 x 1.75
M14 x 2.0
M16 x 2.0
M18 x 2.5
M20 x 2.5
M22 x 2.5
4.8
6.8
8.8
10.9
<Table 4>
12.9
600
960
1493
2054
2912
3960
800
1280
1990
2740
3880
5276
1310
2075
3240
4455
6340
8613
6.8
43.7
