Bolt torque, General bolt tightening torque – Martin Sprocket & Gear Bucket Elevator Safety User Manual
Page 17
Bolt Torque
13
General Bolt Tightening Torque
Thread
Tensile Stress
Area
SAE Grade 2
SAE Grade 5
SAE Grade 8
Size
Tsa
75% Yield Strength (PSI) - 43000
75% Yield Strength (PSI) - 69000
75% Yield Strength (PSI) = 98000
Plain
Zinc Plated
Plain
Zinc Plated
Plain
Zinc Plated
Square Inches
Ft.Lb.
Ft.Lb.
Ft.Lb.
Ft.Lb.
Ft.Lb.
Ft.Lb.
1/4-20.
0.0318
6
6
9
10
13
14
1/4-28.
0.0364
7
7
10
12
15
16
5/16-18.
0.0524
12
13
19
21
27
29
5/16-24.
0.0580
13
14
21
23
30
33
3/8-16.
0.0775
21
23
33
37
47
52
3/8-24.
0.0878
24
26
38
42
54
59
7/16-14.
0.1063
33
37
53
59
76
83
7/16-24.
0.1187
37
41
60
66
85
93
1/2-13.
0.1419
51
56
82
90
116
127
1/2-20.
0.1599
57
63
92
101
131
144
9/16-12.
0.1820
73
81
118
129
167
184
9/16-18.
0.2030
82
90
131
144
186
205
5/8-11.
0.2260
101
111
162
179
231
254
5/8-14.
0.2560
115
126
184
202
261
287
3/4-10.
0.3340
180
197
288
317
409
450
3/4-16.
0.3730
200
221
322
354
457
503
The reason all applications should be evaluated to determine the optimum tightening torque is that the K
factor in this formula is always an estimate.
The most commonly used bolting K factors arc 0.20 for plain finished bolts, 0.22 for zinc plated bolts,
and 0.10 for waxed or highly lubricated bolts
Formula: T= K x D x P
• T
Target tighten torque (the result of this formula is in inch pounds, dividing by 12 yields foot pounds
• K
Coefficient of friction (nut factor), always an estimation in this formula
• D
Bolts nominal diameter in inches
• P
Bolt's desired tensile load in pounds (generally 75% of yield strength) - [ P(lbs) = (75%) Yield
Strength * Tensile Stress Area ]