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7-2. Tightening Torque
7-2-1. Tightening torque characteristic comparisons
Thanks to the high-power rare-earth magnet motor and the larger hammer inertia, the Model WH 14DM can
provide greater tightening torque.
kgf
cm
N
m
•
•
160
1600
(1389 in-lbs.)
140
1400
(1215 in-lbs.)
120
1200
(1042 in-lbs.)
100
1000
(868 in-lbs.)
80
800
(694 in-lbs.)
60
600
(521 in-lbs.)
400
40
(347 in-lbs.)
200
20
(174 in-lbs.)
0
0
0 0
7-2-2. Screw diameter and appropriate tightening torque
Generally speaking, the appropriate tightening torque for a screw can be determined by the strength grade of the
screw and the material tightened. Tables 1 and 2, and Fig. 3 below list data relative to the strength grade of
various screws 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= 9.8 k
d
p/100
•
•
T: Appropriate tightening torque (N
k: Torque coefficient (0.17)
d: Nominal diameter for the screw (mm)
p: Recommended axial tightening force to be applied to the screw (kgf)
p=rated axial stress (kgf/mm
•
Strength grade and rated axial stress of threads
Strength grade
Rated axial stress (kgf/mm
Material
Heat treatment
•
Diameter and effective sectional areas of threads
Kind of thread (x pitch)
Effective sectional area
2
of thread (mm
)
P
WH 14DM
1
Tightening time
Fig. 2
m)
•
2
) x 0.8 x effective sectional area of the thread (mm
4.8
2
)
29.1
Mild steel
None
Table 2
M5 x 0.8 mm
M6 x 1 mm
(3/16")
(1/4")
14.2
20.1
C
WH 12DM
2
3 (sec.)
Table 1
6.8
43.7
M8 x 1.25 mm
M10 x 1.5 mm
(5/16")
(3/8")
36.6
58.0
--- 8 ---
Test conditions
Bolt: M12 x 45 mm (15/32" x 1-3/4")
(strength grade: 12.9)
Steel plate: Mild steel
Thickness = 25 mm (1")
Accessory tool: Hexagon socket ass'y
2
)
8.8
58.2
Alloy steel including Ni, Mn, Cr, etc.
Processed-hard material
M12 x 1.75 mm
M14 x 2 mm
(15/32")
(9/16")
84.3
115
12.9
95
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