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7-2-2. Bolt tightening torque characteristics
Figure 5 shows relationships between time and tightening torque for individual bolt types and sizes. While the
data are useful for handy reference, actual tightening torque will vary depending on tightening conditions and
other variables. For details, please refer to Para. 8-3, Tightening Torque Variation.
NOTE: The term "tightening time" indicates the impact time after the lower surface of the bolt has come
in contact with the material into which it is being tightened.
In the tightening conditions shown in Fig. 5, the screws are being tightened directly into a steel
plate; accordingly, the torque goes up very abruptly in comparison with ordinary bolt tightening
conditions.
Model WH 14DAF2
Bolt
Nut
Steel plate
thickness: t
* The following bolts were utilized:
Ordinary bolt; strength grade 4.8
High-strength bolt; strength grade 12.9
Strength grade is read as follows:
4.8
Yield point or durable force:
(45,500 psi)
Tensile strength of the bolt:
(56,900 psi)
Washer
Washer
Fig. 5
Tightening time: sec
20
(200)
40
(400)
60
(600)
80
(800)
120
(1200)
(kgf
.
cm)
T
ightening torque
0
1
2
3
0
N
.
m
M10 (t = 10 mm)
M12 (t = 25 mm)
M8 (t = 10 mm)
100
(1000)
Ordinary bolt
Tightening time: sec
20
(200)
40
(400)
60
(600)
80
(800)
120
(1200)
(kgf
.
cm)
T
ightening torque
0
1
2
3
0
N
.
m
M10 (t = 10 mm)
M12 (t = 25 mm)
M8 (t = 10 mm)
100
(1000)
High-strength bolt
