Table of Contents
Advertisement
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. 5 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
N
m
(kgf
cm)
•
•
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)
40
400
(347 in-lbs)
20
200
(174 in-lbs)
0
0
cm)
•
2
) x 0.8 x effective sectional area of the thread (mm
4.8
2
)
29.1
Mild steel
None
M5 x 0.8 mm
M6 x 1 mm
(3/16")
(1/4")
14.2
20.1
6
8
(1/4")
(5/16")
Table 1
6.8
43.7
Table 2
M8 x 1.25 mm
M10 x 1.5 mm
(5/16")
(3/18")
36.6
58.0
Strength grade 12.9
(high-strength bolt)
10
12
(3/8")
(15/32")
Fig. 5
--- 21 ---
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 8.8
(high-strength bolt)
Strength grade 6.8
(ordinary bolt)
Strength grade 4.8
(ordinary bolt)
14
16
(9/16")
(5/8")
12.9
95
M16 x 2 mm
(5/8")
157
mm
Advertisement
Table of Contents
