-12-
7-2-3. Tightening torque characteristics
The graph below shows the relationship between tightening time and tightening torque according to
types of bolts. The data below are intended for reference purposes only because actual tightening
torque may vary depending on tightening conditions.
NOTE:
• The term "tightening time" means the impact time after the lower surface of the bolt comes
in contact with the washer.
• Each bolt is directly tightened into a steel plate under the following tightening conditions.
Accordingly, the torque goes up very abruptly in comparison with the actual bolt tightening
conditions.
Washer
Bolt
Nut
S
teel plate thickness t
Following bolts were used.
Ordinary bolt: Strength grade 4.8
High-strength bolt: Strength grade 12.9
Strength grade is read as follows.
4.8
Yield point of bolt
320 N/mm
2
{32 kgf/mm
2
, 45,500 psi }
Tensile strength of bolt 400 N/mm
2
{40 kgf/mm
2
, 56,900 psi }
T
ighte
n
in
g torqu
e
Tightening time sec.
(Steel plate thickness t = 25 mm)
Ordinary bolt
High-strength bolt
T
ighte
n
in
g torqu
e
Ordinary bolt
High-strength bolt
Tightening time sec.
(Steel plate thickness t = 25 mm)
