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Factors Affecting Tighten-
ing Torque
The tightening torque is affected by a wide
variety of factors including the followings.
After tightening, always check the torque
with a torque wrench.
1) Voltage
When the battery pack becomes near-
ly discharged, the voltage decreases and
the tightening torque drops.
Bolt Tightening Conditions
M12
M14
M16
M10
0.0 0.5 1.0 1.5 2.0 2.5 3.0
196.0
(2000)
147.0
(1500)
98.0
(1000)
49.0
(500)
Tightening time (Sec.)
M10×35 mm M12, M14, M16 ×45 mm
Standard bolt
Tightening torque
N·m
(kgf-cm)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
M12
M10
M8
196.0
(2000)
147.0
(1500)
98.0
(1000)
49.0
(500)
Tightening time (Sec.)
M8, M10×35 mm M12×45 mm
High tensile bolt
Tightening torque
N·m
(kgf-cm)
Bolt
Nut
Washer
Steel plate
thickness10 mm (3/8")
Washer
Spring washer
Tightening conditions
• The following bolts are used.
Standard bolts: Strength type 4.8
High tensile type 12.9
4.8
Explanation of the strength type
Bolt yield point
(80% of tensile strength)
32 kgf/mm
2
(45000psi)
Bolt tensile strength
40 kgf/mm
2
(56000psi)
2) Tightening time
Longer tightening time results in increased
tightening torque. Excessive tightening, how-
ever, adds no value and reduces the life of
the tool.
3) Different bolt diameters
The size of the bolt diameter affects the tight-
ening torque.
Generally, as the bolt diameter increases,
tightening torque rises.
4) Tightening conditions
Tightening torque will vary, even with the
same bolt, according to grade, length, and
torque coefficient (the fixed coefficient indi-
cated by the manufacturer upon produc-
tion).
Tightening torque will vary, even with the
same bolting material (e.g. steel), accord-
ing to the surface finish.
Torque is greatly reduced when the bolt
and nut start turning together.
5) Socket play
Torque is lowered as the six-sided configu-
ration of the socket of the wrong size is
used to tighten a bolt.
6) Switch (Variable speed control trigger)
Torque is lowered if the unit is used with
the switch not fully depressed.
7) Effect of Connecting Adaptor
The tightening torque will be lowered
through the use of a universal joint or a
connecting adaptor.
EY7541(UL).indb 12 2007/01/16 9:32:04