TECHNICAL DATA
Bolt Tightening
2
Bolt Tightening
2-1
2-2
2-3
Various Tightening Methods
Various tightening methods
Screw and Torque
Relation formula between screw and torque
34
35
Torque Coefficient
36
（2）The torque coefficient is not stable 36
（3）Even when the torque is stable, axial tension may vary 36
（1）Formula of torque coefficient
2-4
Method for Determining Tightening Torque
37
（2）Methods for determining tightening torque 37
（3）Standardize the tightening torque 38
（4）Standard tightening torque
40
（1）Applying appropriate tightening torque
2-5
2-6
Tolerance of Tightening Torque
Tolerance of tightening torque
Tightening of Tension Stability
（1）Zigzag tightening
（2）Two steps tightening
（3）Two times tightening
（4）Stabilized tightening
32
42
43
43
43
43
TOHNICHI TORQUE HANDBOOK Vol.9
TECHNICAL DATA
2
Torque and Tension
Bolt Tightening
Why tighten screws?
Screw tightening is carried out in order to stop
objects from moving (to fix them). Followings are
major objectives of the screw tightening.
1. For fixing and jointing objects
2. For transmitting driving force and braking force
3. For sealing drain bolts, gas and liquid
The fixing force at this time is called the axial
tension (tightening force), and the target of screw
tightening is to“apply an appropriate axial tension.”
Although axial tension control should normally
be carried out, because axial tension is difficult to
measure, torque control is used for its substitute
characteristics that allow tightening administration
and operations to be carried out easily.
Axial
tension
Figure 2-1.
Enhance reliability with
combination of fixing,
transmitting, preventing
leakage and others.
Technical Data
33
Various Tightening Methods
Various tightening methods
Table 2-1. Various tightening methods
Tightening method
Torque control
method
Description
Advantages and disadvantages
Bolt tightening is controlled by specific It is reasonable way for tightening control and operation.
torque value.
Tightening torque is not influenced by the bolt length so
This is the most widely used method. easy to standardize. The Bolt efficiency will be low due to
wide tolerance of the tension.
The tightening is managed by rotting
angle which start from the seating
point of the bolt head.
Tightening is conducted by specific
angle from the snug torque.
Tightening within plastic zone gives lower dispersion of axial
tension and easy the operation.
Since tightening conducts beyond the yield point, there is
limitation for additive load to the joint or difficulty for retightening. It is difficult to define the tightening angle.
The tightening is managed by the
variation of the torque gradient
against rotating angle at the yield
point.
The variation is monitored and
carried out arithmetic process by an
electronic device.
Since the dispersion of the axial tension is small, it is possible
to design the bolt efficiency large.
Inspection for the bolt itself is possible even after tightening.
Tightening is conducted beyond the yield point and the
tightening device is expensive, so it is hard to adopt the
same method in the service field.
Elongation
measurement
method
Tightening is controlled by the elongation
of the bolt, generated by bolt tightening.
Elongation is measured by a micrometer,
ultrasonic, or an embedded gauge
sensor in a bolt.
The dispersion of the bolt is very small. Tightening within the
elastic zone is available. The efficiency of the bolted joint is
large. Additive loading and bolt re-tightening are possible.
The bolt end faces must be finished. The tightening cost is
high.
Loading
method
By tightening the nut while tensile
load is applied to the bolt, tightening
is controlled by the generated tensile
force after releasing the load.
Axial tension can be directly controlled.
Torsion stress of the bolt is not generated.
The tightening device and bolts are specially made. High
cost.
Heating
method
Tightening is controlled by the
variation of the elongation before and
after heating the bolt.
Space and force are not required for tightening.
There is no clear relation between the heat and axial
tension. Temperature setting control is difficult.
Rotation angle
method
Torque gradient
method
Figure 2-2. Tightening control methods
Rotation angle method
Torque gradient method
Axial tension
TECHNICAL DATA
Bolt Tightening
2
2-1
Bolt Tightening
Torque control
method
Yield point
Elastic zone
34
Break point
Plastic zone
TOHNICHI TORQUE HANDBOOK Vol.9
TECHNICAL DATA
Screw and Torque
Relation formula between screw and torque
Figure 2-3.
Detail drawing
Relational drawing
α
β
Tension Ff
10%
Friction on the
bearing surface
50%
Formula of screw (1)
Reference literature: "Theory and calculation of threaded fasteners"
Akira Yamamoto (Yokendo Co., Ltd.)
d²
2
T= Ff
μ
dn
+ tanβ + μn
÷1000
2
cosα
Friction on the threaded portion Tension Ff Friction on the bearing surface
ｄ2
ｄ
T : Torque ････････[N・m]
Friction on the
threaded portion
40%
Example: For a M8 bolt at Ft = 8000 [N], the tightening torque is
From P.132 Table 8-1.
F : Axial tension ･･･ [N]
d² : Pitch diameter [mm]（See P.132 Table 8-1)
dn : Pitch diameter of bearing surface
･･････････････････ [mm]（See P.132 Table 8-1）
μ : Friction coefficient of threaded portion
･･････････････････（See P.36 Table 2-2）
μn : Friction coefficient of bearing potion
･･･････････････････
（See P.36 Table 2-2）
α : Half angle of screw thread · ISO Screw 30°
d2 = 7.188 [mm]
dn1 = 11.96 [mm] (Hexagon nut style)
tanβ = 0.0554
From P.36 Table 2-2.
μ = μn = 0.15 α = 30゜
T = 8000{ 7.188 ( 0.15 ＋ 0.0554) ＋ 0.15( 11.96 )} ÷ 1000
2
cos30 ゜
2
= 13.8［N・m］
a. Hexagon bearing surface (first type nut, bolt)
0.608B3 − 0.524dH3
β : Lead angle [tan β ] ･（See P.132 Table 8-1）
dn1 =
■ Formula of pitch diameter
of bearing surface (dn¹, dn)
B: Hexagon width across flats [mm] dH: Bearing surface inside diameter [mm]
B
dH
Figure 2-4.
0.866B2 − 0.785dH2
b. Round shape bearing surface (second, third type nut)
dn =
2
3
・
D3 − dH3
D2 − dH2
D: Bearing surface outside diameter [mm] dH: Bearing surface inside diameter [mm]
dn1
Formula of screw (2)
T
K d
K: Torque coefficient (See P.36 Table 2-2)
T = K.d.Ff or Ff =
d: Nominal size of screw [mm]
dn
Example: Axial tension to tighten a M20 screw to T = 400 [N・m]
dH
D
Technical Data
d =20［mm］K = 0.2 (See P.36 Table 2-2)
400
F=
＝ 100000［N］
0.2 × 20 ÷ 1000
35
2
Bolt Tightening
2-2
Bolt Tightening
Torque Coefficient
（1）Formula of torque coefficient
K＝
1
d2
2d
μ
＋tanβ ＋μn・dn
cosα
（2）Variable Torque Coefficient
Table 2-2. Torque coefficient and friction coefficient
Torque coefficient Friction coefficient
Min. - Avg. - Max. Min. - Avg. - Max.
General machine oil
Spindle oil
Machine oil
Turbine oil
Cylinder oil
0.14〜0.20〜0.26
Low friction oil
Double sulfurous
molybdenum
Wax based oil
0.10〜0.15〜0.20
Fcon
Bolt tension
stabilization
(See P.482)
0.16〜0.18〜0.20
0.10〜0.15〜0.20
● Machine factors of the bolted Joint
Lubrication
Environment ● Tightening speed
● Reutilization screw
●
Figure 2-5. Relation between tightening torque and
tightening axial tension
Max. tension
Ffmax
Fs
Kmin.
（Min. torque coefficient）
Min. tension
Ffmin
0.067〜0.10〜0.14
Kmax.
（Max. torque coefficient）
0.12〜0.135〜0.15
Note: The values in this table are for standard screw
joints. They are not applicable for special
conditions.
K ≈ 1.3μ + 0.025
Min. and max. indicate the width of dispersion
(± 3σ). The variation width will be smaller if the
conditions are limited. (by lubrication oil, shape, etc.)
36
■ Factors of fluctuated axial tension
●
d is the nominal screw diameter [mm]
Lubrication
（3）Fluctuated axial tension with
same applied torque
Tension
TECHNICAL DATA
Bolt Tightening
2
2-3
Bolt Tightening
Applied torque
Tightening torque
Example: Applying same torque value, how
the axial tension varies when the
torque coefficient is changed.
F = T / (K.d)
Nominal diameter: d = 10 [mm] = 0.01 [m]
Tightening torque: T = 24 [N・m]
Torque coefficient: Kmin. = 0.14, K = 0.2, Kmax. = 0.26
Kmin. = 0.14
Fmax＝24 / (0.14×0.01) ＝17140［N］
Kmax. = 0.26
Fmin＝24 / (0.26×0.01) ＝9230［N］
K = 0.2
Fs＝24 / (0.2×0.01) ＝12000［N］
TOHNICHI TORQUE HANDBOOK Vol.9
Method for Determining Tightening Torque
（1）Applying appropriate tightening torque
｝
Fu > Fmax
｛
~ Ffs ~ Ffmin > FL
2
Fixing
Sealing
Transmission
Looseness
Bolt Tightening
Male screw strength
Female screw strength
Strength of bolted joint
Bearing surface strength
Figure 2-6. Applying appropriate tightening torque
Bearing surface
Transmission
Female screw
Looseness
Bolted joint
Male screw
Fu
Fixing
Fs
Ffmax
Ffmin
Excess tightening
Leakage
FL
Insufficient tightening
（2）Methods for determining tightening torque
Table 2-3. Methods for determining tightening torque
1. Standardization
To establish company
standardization of tightening torque.
(See P.38 Figure 2-8)
2. Confirmation
of the present
tightening torque
To establish the present
tightening torque and confirm it.
3. Method based on
breaking torque
(Determination of
upper limit)
To adopt 70% of the breaking
torque as the tightening
torque for screw joints.
(Ffmax = Fu)
4. Method based
on axial tension
(Determination of
lower limit)
To adopt 130% of the minimum
required tightening torque, the
level that prevents loosening, as
the tightening torque. (Ffmin = FL)
5. Method based
on axial tension
measurement
To specify the tightening torque as
the optimal axial tension by measuring
with an axial tension meter.
Technical Data
Figure 2-7. Various defective joints
Method based on breaking torque point
Fu=Fmax
Fs
Fmin
FL
30%
Method based on minimum required torque
Fu
TECHNICAL DATA
2-4
Bolt Tightening
Fmax
Fs
FL=Fmin
30%
37
Method for Determining Tightening Torque
（3）Standardization of Tightening Torque
■ Relation between Screw and Torque
Calculation formula
T = K・d・F (JIS B 1083)
d +d 2
As = π（ ² ³） (JIS B 1082)
4
2
d³ = d1- H
6
H = 0.866025P
σ=
F
As
T：Tightening torque [N.m]
K：Torque coefficient 0.2 ( μ ≈ 0.15)
d：Nominal diameter of bolt [mm]
F : Axial tension [N]
As: Stress area of bolt [mm²]
(JIS B 1082)
Torque
Bolt Tightening
2
Figure 2-8. Relation between screw and torque
Nominal diameter of bolt (d [mm])
TECHNICAL DATA
2-4
Bolt Tightening
d² : Effective diameter of bolt [mm]
(JIS B 0205)
d³： Value of 1/6 of fundamental triangle
height subtracted from root diameter
of bolt (d¹) [mm]
d¹：Root diameter of bolt [mm]
(JIS B 0205)
H：Fundamental triangle height [mm]
P：Pitch [mm]
σ： Tensile stress of bolt [N/mm²]
Stress
[N/mm2］
38
Tightening torque
series
Brass
Carbon steel
TOHNICHI TORQUE HANDBOOK Vol.9
TECHNICAL DATA
Table 2-4. Standard tightening torque [N・m]
Nominal diameter
M1
(M1.1)
(M1.2)
(M1.4)
M1.6
(M1.8)
M2
(M2.2)
M2.5
M3
(M3.5)
M4
(M4.5)
M5
M6
(M7)
M8
M10
M12
M14
M16
(M18)
M20
(M22)
M24
(M27)
M30
(M33)
M36
(M39)
M42
(M45)
M48
(M52)
M56
(M60)
M64
(M68)
T
［N・m］
0.0193
0.0272
0.0369
0.0578
0.0853
0.129
0.174
0.229
0.356
0.634
0.997
1.48
2.14
2.98
5.07
8.50
12.3
24.4
42.5
67.6
106
145
206
280
356
521
707
962
1240
1600
1980
2480
2960
3840
4780
5950
7200
8740
(Reference value)
0.5T series 1.8T series 2.4T series
［N・m］
［N・m］
［N・m］
0.00965
0.0347
0.0136
0.0490
0.0185
0.0664
0.0289
0.104
0.0427
0.154
0.0645
0.230
0.0870
0.310
0.115
0.410
0.178
0.640
0.317
1.14
0.499
1.79
0.740
2.66
1.07
3.85
1.49
5.36
2.55
9.18
4.25
15.3
6.15
22.1
12.2
43.9
21.3
76.5
33.8
122
53.0
190
73.0
263
102
367
140
504
178
641
261
938
354
1270
481
1730
620
2230
800
2880
990
3560
1240
4460
1480
5330
1920
6910
2390
8600
2950
10700
3600
13000
4400
15700
0.0463
0.0653
0.0886
0.139
0.204
0.310
0.418
0.550
0.854
1.52
2.39
3.55
5.14
7.15
12.2
20.4
29.5
58.6
102
162
254
350
490
672
854
1250
1700
2310
2980
3840
4750
5950
7100
9220
11500
14300
17300
21000
Standard bolt stress: 210 [N/mm2] Stress area of bolt
Round the digit to effective 3 digits.
Table 2-5. Standard tightening torque [kgf・cm] (Reference value)
Nominal diameter
M1
(M1.1)
(M1.2)
(M1.4)
M1.6
(M1.8)
M2
(M2.2)
M2.5
M3
(M3.5)
M4
(M4.5)
M5
M6
(M7)
M8
M10
M12
M14
M16
(M18)
M20
(M22)
M24
(M27)
M30
(M33)
M36
(M39)
M42
(M45)
M48
(M52)
M56
(M60)
M64
(M68)
T
0.5T series 1.8T series 2.4T series
［kgf・cm］ ［kgf・cm］ ［kgf・cm］ ［kgf・cm］
0.197
0.277
0.376
0.589
0.870
1.32
1.77
2.34
3.63
6.47
10.2
15.1
21.8
30.4
51.7
86.7
125
249
433
689
1080
1480
2100
2860
3630
5310
7210
9810
12600
16300
20200
25300
30200
39200
48700
60700
73400
89100
0.0984
0.354
0.139
0.500
0.187
0.677
0.293
1.06
0.435
1.57
0.658
2.37
0.887
3.19
1.17
4.20
1.82
6.53
3.23
11.6
5.09
18.3
7.55
27.1
10.9
39.3
15.2
54.7
26.0
93.6
43.3
156
62.7
225
124
448
217
780
345
1240
540
1940
744
2680
1040
3740
1430
5140
1820
6540
2660
9560
3610
13000
4900
17600
6320
22700
8160
29400
10100
36300
12600
45500
15100
54400
19600
70500
24400
87700
30100
109000
36700
133000
44900
160000
0.472
0.666
0.903
1.42
2.08
3.16
4.26
5.61
8.71
15.5
24.4
36.2
52.4
72.9
124
208
301
598
1040
1650
2590
3570
5000
6850
8710
12700
17300
23600
30400
39200
48400
60700
72400
94000
117000
146000
176000
214000
Multiply the table(N・m) on the left by 10.1972 and
rounded to effective 3 digits.
■ Screws and applicable“T”series
Table 2-6. Screws and applicable“T”series
Applicable screws
(Strengths) (Material)
Standard T series
0.5T series
Axial tension standard value
[N/mm2] Min - Max
4.6 〜 6.8
SS, SC, SUS
210
160 〜 300
ｰ
Brass, Copper, Aluminum
Application
To be applied to ordinary
screws, unless otherwise
specified
Male and female screws
with copper, aluminum or
plastic, for die-cast plastic
products
Applicable products
Ordinary products
Electronic products
105
80 〜 150
1.8T series
8.8 〜 12.9
SCr, SNC, SCM
380
290 〜 540
2.4T series
10.9 〜 12.9
SCr, SNC, SCM, SNCM
500
380 〜 710
Durable screw joints made of special steel including
those affected by additional dynamic loads
(Friction clamping)
Vehicles, Engines
Construction products
＊The maximum to the minimum of the axial stress is considered as the dispersion of the torque coefficient.
Example: σ max = 210 × (0.2 ÷ 0.14) = 300 [N/mm2]
Torque coefficient: 0.14 (minimum)〜0.2 (average) 〜 0.26 (maximum)
Technical Data
39
2
Bolt Tightening
■ Standard tightening torque
TECHNICAL DATA
2-4
Bolt Tightening
Method for Determining Tightening Torque
（4）Standard tightening torque
M1
(M1.1)
(M1.2)
0.460
0.588
0.732
0.0193
277
744
2.14
2380
(M4.5)
M5
M6
(M7)
M8
M10
M12
M14
M16
(M18)
8.78
11.3
1.48
14.2
2.98
28.9
8.50
20.1
36.6
58.0
84.3
115
157
192
5.07
12.3
24.4
42.5
67.6
106
145
M20
245
206
M24
353
356
561
707
817
1240
1120
1980
(M22)
303
(M27)
459
(M33)
694
M30
M36
(M39)
M42
(M45)
M48
(M52)
M56
(M60)
M64
(M68)
976
280
521
962
1600
1060
0.317
4670
17400
9390
12.2
18600
33.8
31000
73.0
7690
12200
17700
24100
25500
51500
73600
39600
74200
106000
63600
96500
118000
146000
2680
3060
7200
8740
6100
8710
4690
17200
9290
6.15
21.3
53.0
102
140
138000
74200
261
208000
112000
427000
496000
563000
643000
804000
918000
19600
37100
53000
1240
433000
494000
3600
4400
1920
2950
31800
15600
147000
2390
381000
610000
36400
103000
328000
708000
25500
800
1480
284000
12700
29000
104000
237000
527000
23700
72900
990
212000
16600
20300
481
354
181000
394000
6830
37200
337000
440000
12700
2960
69000
236000
308000
8880
12100
5490
1640
2340
48300
90600
158000
3840
3040
24500
620
293000
2130
1150
45500
178
132000
205000
Min. axial tension
4340
49000
168000
915
3040
2.55
2130
712
4.25
90900
57100
1320
406
1490
246000
369000
5950
57500
755
201
1.49
172000
3840
4780
13600
47300
1760
2030
25300
34500
5910
33100
40300
276000
2960
11000
3250
548
1700
8670
6040
103
138
274
1190
1.07
925
59.3
79.4
509
1020
0.740
37.1
47.6
167
713
528
Fmin
［N］
311
0.499
2290
1830
218
191
356
4260
4230
Max. axial tension
813
133
0.178
2980
6070
Std. axial tension
373
0.0870
1430
2480
2360
261
335
0.0427
2640
3400
110
0.115
205
1850
1310
1470
1510
88.3
400
1100
1420
0.634
77.1
68.9
256
2040
0.997
61.8
179
548
6.78
0.0185
48.3
0.0645
1020
(M3.5)
0.0136
Fmax
［N］
147
712
621
0.00965
Fs
［N］
103
435
520
［N・m］
0.0289
0.174
0.229
381
118
159
267
0.356
M4
220
95.1
0.0853
3.39
5.03
Min. axial tension
512
154
M2.5
M3
Max. axial tension
358
0.129
2.07
Std. axial tension
295
1.70
2.48
74.2
206
0.0369
(M1.8)
M2
137
177
Fmin
［N］
124
0.0578
(M2.2)
96.5
Fmax
［N］
0.0272
0.983
1.27
Fs
［N］
0.5T series
Std. tightening torque
［N・m］
(M1.4)
M1.6
40
［mm2］
T series
Std. tightening torque
Bolt Tightening
Nominal diameter
2
Stress area of bolt
Table 2-7. Standard tightening torque and bolt axial tension
59000
86100
118000
138000
28500
84300
45400
123000
66200
168000
90700
56100
78900
197000
106000
185000
264000
142000
246000
351000
154000
213000
281000
324000
220000
119000
305000
164000
402000
462000
216000
249000
189000
TOHNICHI TORQUE HANDBOOK Vol.9
TECHNICAL DATA
(M1.2)
(M1.4)
M1.6
(M1.8)
M2
(M2.2)
M2.5
M3
(M3.5)
M4
(M4.5)
M5
M6
(M7)
0.0490
0.983
0.104
0.732
1.27
M20
(M22)
M24
1120
0.640
644
936
1280
1900
2560
11.3
3.85
4280
20.1
9.18
28.9
58.0
115
157
192
245
303
353
2.66
5.36
3330
263
70600
M64
(M68)
2680
3060
Technical Data
4120
8410
16900
33500
1050
1490
804
1710
2440
1310
3410
4880
2630
8160
4390
14500
7820
861
1250
1.52
2530
3.55
4440
2.39
5.14
7.15
12.2
5710
7150
10200
20.4
14600
58.6
29300
29.5
113000
490
123000
854
178000
254000
1700
283000
405000
5330
8600
13000
15700
555000
768000
1020000
1150000
326000
793000
427000
1100000
591000
949000
1270000
1450000
1650000
511000
686000
781000
888000
4750
231000
350000
414000
565000
7100
740000
11500
17300
21000
9220
14300
22500
32700
117000
661000
605000
11200
14200
218000
5950
496000
5500
153000
381000
424000
3410
74800
708000
3560
2980
1950
139000
492000
2310
962
97200
3840
238000
1250
662
44500
284000
442000
672
41900
382
82700
527000
310000
350
57900
369000
2230
163000
20800
79400
162
202000
302000
10200
254
374000
212000
6340
60700
262000
1270
3620
42500
1730
103000
1790
26300
134000
191000
1230
18400
102
Min. axial tension
490
248000
134000
88100
Max. axial tension
Std. tightening torque
Std. axial tension
911
638
0.550
0.854
178
228
284
174000
641
56200
0.310
Fmin
［N］
527
938
91800
892000
2360
62200
709
369
164000
504
10700
(M60)
31400
496
115000
367
664000
2030
15600
0.139
0.0886
104000
6910
M56
Min. axial tension
131000
7660
331
424
73100
1760
1470
2560
45700
4460
M48
4750
1970
84800
43600
59400
1310
(M52)
1460
24500
2880
1120
2710
3650
985
45500
976
M42
720
1830
232
Fmax
［N］
297
0.418
31900
(M39)
(M45)
1340
Fs
［N］
0.0653
602
10600
694
817
496
0.0463
0.204
19700
(M33)
M36
921
［N・m］
370
13800
459
561
286
5890
22000
122
213
531
10900
5360
43.9
190
171
7650
10900
76.5
134
3290
15.3
22.1
Fmin
［N］
6110
(M27)
M30
Max. axial tension
Std. axial tension
783
0.310
371
1.79
84.3
(M18)
688
1.14
M12
M16
481
5.03
14.2
318
0.154
0.410
8.78
248
395
2.48
6.78
174
223
Fmax
［N］
277
0.230
3.39
Fs
［N］
0.0664
1.70
2.07
36.6
M14
0.0347
0.588
M8
M10
［N・m］
2
2.4T series
175000
61100
94200
137000
331000
178000
500000
269000
703000
379000
944000
509000
591000
808000
218000
318000
435000
1060000
569000
1030000
1470000
790000
1350000
1540000
1930000
2210000
887000
1190000
1270000
1700000
Bolt Tightening
0.460
Std. tightening torque
Stress area of bolt
Nominal diameter
M1
(M1.1)
［mm2］
1.8T series
682000
917000
1040000
1190000
41
TECHNICAL DATA
Bolt Tightening
2
2-5
Bolt Tightening
Tolerance of Tightening Torque
Tolerance of Tightening Torque
For threaded joints, sometimes more definite tightening control is necessary, while at other times
relatively rough control is adequate just so that joints will not loosen. The axial tension will be
influenced by the dispersion of the torque coefficient and the tolerance of the tightening torque.
In order to limit the axial tension dispersion, it will be meaningless simply to limit the tightening
torque tolerance without also limiting the torque coefficient dispersion.
■ Tolerance of tightening torque
Table 2-8.
Class
Special
Tightening torque
Torque value
｝
Torque coefficient
Tolerance
Coefficient
｝
Dispersion
Upper/lower
limit (Ratio)
±15％
±15％ 115〜85％
0.75
±20％
±20％ 120〜80％
0.65
2nd class Standard torque（measured value） ±20％
0.14〜0.26※
（0.10〜0.20） ±30％
±35％ 135〜65％
0.50
3rd class
0.12〜0.28※
（0.09〜0.20） ±40％
±50％ 150〜50％
0.35
1st class
Measured value
Standard torque
±5％
Axial tension
Tolerance
Measured value
±10％
±30％
※
（ ）Values in brackets are when using disulfide molybdenum or wax as lubrication.
■ Relation formula of standard deviation
When you require strict bolt management, the
In order to make σnsmaller, it is necessary to
using the standard deviation（ %）of the
is easy to manage the tightening torque, σk ≈
following formulas express the relationships
dispersion of the tightening torque and the
torque coefficient.
make σk and σt smaller, respectively. Since it
σt will be set if σk = 1/3 σt is approximately
controlled.
Dispersion in axial tension (σn),
Example:
torque coefficient (σk), and tightening
K = 0.2 ± 0.06（3σ）
0.06
σK =
×100（％）=10（％）
3×0.2
σt = 3％
torque (σt) relation
σｎ＝ σｋ2 ＋σt2
σn = 102 ＋ 32＝10.4％
（3σn = 31.2％）
42
TOHNICHI TORQUE HANDBOOK Vol.9
TECHNICAL DATA
Tightening of Tension Stability
Tightening Procedures
2
Various tightening methods for stabilizing the initial axial tension have been devised.
（1）Zigzag tightening
（3）Two times tightening
It is recommended
In the case where there will be a delay for
diagonal sequence
initial axial tension will not be obtained,
drawing.
packing or rubber in the flap tightened, this is
axial tension transmission and adequate
to tighten nuts in a
such as due to an existing soft part such as
as shown in the
a method of securing initial axial tension by
first tightening the nuts with 100% torque and
Figure 2-9.
First time…T i g h t e n t o a r o u n d 5 0 % o f t h e
specified torque in turns.
Second time…Tighten to around 75% of the
specified torque in turns.
Third time…Tighten to 100% of the specified
torque in turns.
It is recommended to tighten all the bolts
equally, and to avoid applying torque to one
then tightening them once more with 100%
torque.
（4）Stabilized tightening
When the bearing will be deformed (including
burr and surface roughness) by the tightening,
this is a method of preventing initial axial tension
drop by tightening the nuts with 100% torque,
then loosening them and tightening them once
more with 100% torque.
or several bolts on one side.
（2）Two steps tightening
The tightening sequence will not follow
this drawing if tightening will be done using
multiple automatic nutrunners. In the first step
the nuts should be tightened provisionally.
(50% of the tightening torque)
Next the final tightening should be done
with 100% torque. The method consists of
tightening in two steps.
Technical Data
43
Bolt Tightening
2-6
Bolt Tightening