High Strength Torque Shear Bolts (also known as Twist-off Bolts) are commonly abbreviated as TC, which originates from the English abbreviation TCB (Tension Control Bolts) to differentiate them. The ends of these bolts have a spline end and the bolt heads are generally circular (mushroom-shaped) with a spline design. A torque shear-style high-strength bolt assembly consists of one high-strength bolt, one nut, and one washer.
The specifications of the steel structure torque shear style high strength bolts range from M16 to M30 (available in six different thread sizes: M16, M20, M22, M24, M27, M30), with lengths ranging from 40mm to 220mm. The performance grades include 10.9 and 12.9s, and the surface treatments can be phosphatized, plain, galvanized, or blackened. The performance indicators comply with the GB/T 3632-2008 standard for torque shear-style high-strength bolts.
Torque Shear Bolt Dimension Details
Product specifications:
Specification range: M16 ~ M30 Material: 20MnTiB and 35VB alloy steel Surface treatments: Blackening, hot-dip galvanizing, and Dacromet coating
During the installation of torque shear-style high-strength bolt connections, only one washer should be added on the side of the nut. The formula for calculating the initial torque value is: Tc = 0.065 * Pc * d, where Tc is the initial torque value in N·m, Pc is the construction pretension in kN, and d is the diameter of the high-strength bolt thread in mm. The final tightening is done using a wrench until the spline end breaks. Emphasis should be placed on quality inspection during the construction process supervision. Torque shear-style high-strength bolts are an improved version of large hexagon high-strength bolts for better construction. Large hexagon high-strength bolts consist of one bolt, one nut, and two washers, while torque shear-style high-strength bolts consist of one bolt, one nut, and one washer.
Features of Structural Torque Shear Bolts:
The bolt’s manufacturing process, including the head, tail, thread, and groove, is all carried out in the same factory using cold forging. The precision and stability of the manufacturing process are excellent.
Continuous steel strip heat treatment furnaces are used for heat treatment. Standard temperature and carbon concentration are automatically recorded to effectively control quenching temperature and gas concentration, preventing carburization or decarburization and ensuring the required mechanical properties of the bolts.
Process control is thoroughly implemented through the use of control charts and process capability analysis methods to track processing and quality conditions, providing comprehensive data for engineering designers’ reference.
Considering the special characteristics of torque shear-style bolts, to prevent sliding and spinning during installation, an anti-slip treatment is added beneath the bolt head during the design and manufacturing process. This effectively avoids safety and quality accidents caused by improper installation due to bolt slippage.
Dimension of High Strength (10.9) Structural Torsion Shear Bolt
Thread d
M16
M20
M22
M24
M27
M30
Thread pitch
2
2.5
2.5
3
3
3.5
da
max
18.83
24.4
26.4
28.4
32.84
35.84
ds
max
16.43
20.52
22.52
24.52
27.84
30.84
min
15.57
19.48
21.48
23.48
26.16
29.16
dw
min
27.9
34.5
38.5
41.5
42.8
46.5
dk
max
30
37
41
44
50
55
k,
Norminal
10
13
14
15
17
19
max
10.75
13.9
14.9
15.9
17.9
20.05
min
9.25
12.1
13.1
14.1
16.1
17.95
k’
min
12
14
15
16
17
18
k"
max
17
19
21
23
24
25
r
min
1.2
1.2
1.2
1.6
2
2
db
max
11.3
14.1
15.6
16.9
19.3
21.4
min
11
13.8
15.3
16.6
18.7
20.8
dc ≈
12.8
16.1
17.8
19.3
21.9
24.4
de ≈
13
17
18
20
22
24
Torsion Shear Bolt Mechanical Property
Mechanical Property
Tensile Strength
Yield Strength σ0.2
Elongation δ5
Shrinkage Ψ
σь
Mpa
%
%
Mpa
min
10.9S
1040~1240
940
10
42
8.8S
830~1030
660
12
45
Torsion Shear Bolt Physical Tensile Load
Thread Size d
M16
M20
M22
M24
M27
M30
Stress cross-sectional area(mm2)
157
245
303
353
459
561
Tensile Load KN
10.9S
163~195
255~304
315~376
367~438
477~569
583~696
8.8S
130~162
203~252
251~312
293~364
381~473
466~578
When the bolt l/d≤3, if the wedge load test cannot be done, the core hardness test is allowed. The core hardness value should comply with the table below.
Tensile Strength
Rockwell Hardness
Vickers Hardness
HRC
HV30
min
max
min
max
10.9S
33
39
312
367
8.8S
24
31
249
296
Fastening Axial Force of Torsional Shear Bolt
Thread d
M16
M20
M22
M24
M27
M30
Average value of each batch of fastening axial force (kN)
Pitch
110
171
209
248
319
391
min
100
155
190
225
290
355
max
121
188
230
272
351
430
Standard Deviation of Fastening Axial Force ≤ /kN
10
15.5
19
22.5
29
35.5
When l is less than the value in the table below, the fastening axial force test may not be carried out. The unit is: millimeter (mm)
Thread d
M16
M20
M22
M24
M27
M30
L
50
55
60
65
70
75
Steel Materials for Structural Bolt Nut and Washer