Hitachi WH 14DMR Technical Data And Service Manual page 20

7-3-2. 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. 4 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=k d p
• •
T: Appropriate tightening torque (kgf
d: Nominal diameter for the screw (mm)
p: Recommended axial tightening force to be applied to the screw (kgf)
p=rated axial stress (kgf/cm
k: Torque coefficient (0.17)
•
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
of thread (mm 2 )
•
Thread diameter and appropriate tightening torque
kgf . cm
3000
(2604 in-lbs.)
2500
(2170 in-lbs.)
2000
(1736 in-lbs.)
1500
(1302 in-lbs.)
1000
(868 in-lbs.)
500
(434 in-lbs.)
0
cm)
•
2 ) x 0.8 x effective sectional area of the thread (mm
4.8
2 )
29.1
Mild steel
M5 x 0.8 mm M6 x 1 mm
(3/16") (1/4")
14.2 20.1
N . m
300
250
200
150
100
50
0
6
8
(1/4")
(5/16")
Table 1
6.8
43.7
None
Table 2
M8 x 1.25 mm M10 x 1.5 mm
(5/16") (3/18")
36.6 58.0
10 12
(3/8") (15/32")
Thread diameter
Fig. 4
--- 17 ---
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
Strength grade 12.9
(high-strength bolt)
Strength grade 8.8
(high-strength bolt)
Strength grade 6.8
(ordinary bolt)
Strength grade 4.8
(ordinary bolt)
16
14
mm
(5/8")
(9/16")
12.9
95
M16 x 2 mm
(5/8")
157