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Torque Shear Bolt

Torque Shear Bolt Introduction

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

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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 dM16M20M22M24M27M30
Thread pitch22.52.5333.5
dc ≈12.816.117.819.321.924.4
de ≈131718202224

Torsion Shear Bolt Mechanical Property

Mechanical PropertyTensile StrengthYield Strength σ0.2Elongation δ5Shrinkage Ψ

Torsion Shear Bolt Physical Tensile Load

Thread Size dM16M20M22M24M27M30
Stress cross-sectional area(mm2)157245303353459561
Tensile Load       KN10.9S163~195255~304315~376367~438477~569583~696

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 StrengthRockwell HardnessVickers Hardness

Fastening Axial Force of Torsional Shear Bolt

Thread dM16M20M22M24M27M30
Average value of each batch of fastening axial force (kN)Pitch110171209248319391
Standard Deviation of Fastening Axial Force ≤   /kN1015.51922.52935.5

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 dM16M20M22M24M27M30

Steel Materials for Structural Bolt Nut and Washer

TypeTensile StrengthThread SizeMaterial
Nut8H  10HM12~M3035#
Washer35~45 HRC12~3045#

Torsion Shear Bolt Chemical Composition

20MnTiB0.17~0.240.17~0.371.30~1.600.04~0.10 0.0005~0.0035≤0.035≤0.035
35VB0.31~0.370.17~0.370.50~0.90 0.05~0.120.001~0.004≤0.04≤0.04
35#0.32~0.400.17~0.370.50~0.80   ≤0.035≤0.035
45#0.42~0.500.17~0.370.50~0.80   ≤0.035≤0.035

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