TENSION CONTROL FASTENERS
Tension Control Bolt
Fast installation. Visible completion.
High-strength TC bolt assemblies for bridge, building and heavy structural-steel connections.
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PRODUCT OVERVIEW
Tension Control Bolts for Controlled Structural Fastening
A tension control bolt, commonly called a TC bolt or twist-off bolt, is a high-strength structural fastener designed for friction-type steel connections. Each coordinated assembly contains one high-strength TC bolt, one matching structural nut and one hardened flat washer. During installation, a dedicated shear wrench turns the nut while reacting against the splined tail. When the designed tightening stage is reached, the spline separates at the annular groove, providing a clear visual completion cue.
Matched Assembly
Bolt, nut and washer supplied as one coordinated set.
Repeatable Tightening
Dedicated tooling supports a consistent installation cycle.
Visible Completion
Spline break-off makes the completed tool cycle easy to identify.
Traceable Quality
Batch certificates and axial-force sampling support inspection.
INSTALLATION PRINCIPLE
A Clear Tool Cycle from Tension Control Bolt Engagement to Break-Off
After the matched assembly is inserted through aligned steelwork, the shear wrench engages both the nut and the splined tail. Counter-rotation tightens the nut and develops clamping force. At the intended torsional condition, the spline twists off at the breakneck groove.
STRUCTURE AND DIMENSIONS
Tension Control Bolt Structure Drawing
The structure drawing identifies the head, shank, thread, breakneck groove and splined tail dimensions used in the data. The supplied drawing references GB/T 3632–3633 and uses millimetres. Confirm every drawing symbol, tolerance and contract requirement before manufacture or procurement.
ORDERING OVERVIEW
Product Specifications OF Tension Control Bolt
| Item | Specification |
|---|---|
| Product type | High-strength tension control bolt assembly |
| Referenced standards | GB/T 3632-2008 assembly; GB/T 1229 nut; GB/T 1230 washer |
| Thread range | M16-M30 |
| Common grade | 10.9S |
| Optional grade | 8.8S |
| Bolt materials | 20MnTiB or 35VB alloy steel |
| Surface treatments | Black oxide, hot-dip galvanized or Dacromet |
| Assembly | One TC bolt + one structural nut + one hardened washer |
| Packaging | Cartons |
ENGINEERING DATA
Dimensional Reference of Tension Control Bolt
TC bolt values are shown in millimeters. Confirm symbol definitions and tolerances against the approved drawing and governing standard.
| Dimension | Limit | M16 | M20 | M22 | M24 | M27 | M30 |
|---|---|---|---|---|---|---|---|
| Pitch p | Nom. | 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 |
| ds | 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 | nom. | 10 | 13 | 14 | 15 | 17 | 19 |
| k | max | 10.75 | 13.9 | 14.9 | 15.9 | 17.9 | 20.05 |
| k | 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 |
| db | min | 11 | 13.8 | 15.3 | 16.6 | 18.7 | 20.8 |
| dc | approx. | 12.8 | 16.1 | 17.8 | 19.3 | 21.9 | 24.4 |
| de | approx. | 13 | 17 | 18 | 20 | 22 | 24 |
PERFORMANCE
TC Bolt Mechanical Properties
| Grade | Tensile strength (MPa) | 0.2% proof/yield min. (MPa) | Elongation min. (%) | Reduction of area min. (%) |
|---|---|---|---|---|
| 10.9S | 1040-1240 | 940 | 10 | 42 |
| 8.8S | 830-1030 | 660 | 12 | 45 |
Tensile Load of Full-Size TC Bolt
| Grade / value | M16 | M20 | M22 | M24 | M27 | M30 |
|---|---|---|---|---|---|---|
| Stress area (mm²) | 157 | 245 | 303 | 353 | 459 | 561 |
| 10.9S tensile load (kN) | 163-195 | 255-304 | 315-376 | 367-438 | 477-569 | 583-696 |
| 8.8S tensile load (kN) | 130-162 | 203-252 | 251-312 | 293-364 | 381-473 | 466-578 |
Core Hardness Alternative for Short Bolts
When l/d is 3 or less and a wedge-load test cannot be performed, the TC bolt allows a core-hardness test.
| Grade | HRC min. | HRC max. | HV30 min. | HV30 max. |
|---|---|---|---|---|
| 10.9S | 33 | 39 | 312 | 367 |
| 8.8S | 24 | 31 | 249 | 296 |
PRELOAD REFERENCE
Tightening Axial Force of TC Bolt
The following values of TC bolt describe the batch mean and permitted standard deviation. Testing may be omitted below the listed lengths: M16 50 mm, M20 55 mm, M22 60 mm, M24 65 mm, M27 70 mm and M30 75 mm.
| Value | M16 | M20 | M22 | M24 | M27 | M30 |
|---|---|---|---|---|---|---|
| Nominal batch mean (kN) | 110 | 171 | 209 | 248 | 319 | 391 |
| Minimum batch mean (kN) | 100 | 155 | 190 | 225 | 290 | 355 |
| Maximum batch mean (kN) | 121 | 188 | 230 | 272 | 351 | 430 |
| Maximum standard deviation σ (kN) | 10 | 15.5 | 19 | 22.5 | 29 | 35.5 |
MATERIAL SELECTION
Materials for Structural Bolts, Nuts and Washers
| Component | Grade / hardness | Thread size | Material |
|---|---|---|---|
| Bolt | 10.9S | M12-M24 | 20MnTiB |
| Bolt | 10.9S | M27-M30 | 35VB |
| Bolt | 8.8S | M12-M16 | 35# |
| Bolt | 8.8S | M20-M24 | 20MnTiB |
| Bolt | 8.8S | M27-M30 | 35VB |
| Nut | 8H / 10H | M12-M30 | 35# |
| Washer | 35-45 HRC | 12-30 | 45# |
Chemical Composition of TC Bolt
| Material | C (%) | Si (%) | Mn (%) | Ti (%) | V (%) | B (%) | P max. | S max. |
|---|---|---|---|---|---|---|---|---|
| 20MnTiB | 0.17-0.24 | 0.17-0.37 | 1.30-1.60 | 0.04-0.10 | – | 0.0005-0.0035 | 0.035 | 0.035 |
| 35VB | 0.31-0.37 | 0.17-0.37 | 0.50-0.90 | – | 0.05-0.12 | 0.001-0.004 | 0.04 | 0.04 |
| 35# | 0.32-0.40 | 0.17-0.37 | 0.50-0.80 | – | – | – | 0.035 | 0.035 |
| 45# | 0.42-0.50 | 0.17-0.37 | 0.50-0.80 | – | – | – | 0.035 | 0.035 |
PROCESS EVIDENCE
Controlled Manufacturing and Batch Inspection
The TC bolt is produced by single-factory cold forming for the bolt head, tail, thread and groove, followed by continuous heat treatment with automatic recording of temperature and carbon concentration. Control charts and process-capability analysis support production tracking.
Inspection: maximum lot size of 2,500 sets, with eight assemblies sampled from each lot for axial-force testing and a traceable quality certificate.
STRUCTURAL APPLICATIONS
Built for Demanding Steel Connections
TC bolt assemblies are used where efficient erection, controlled tightening and clear inspection status are important.
Railway and Highway Bridges
Steel Box Girder splices, cross frames and other high-strength friction connections.
Industrial Buildings and Boiler Frames
Large-span plants, boiler frames, pipe racks and heavy structures.
High-Rise Buildings and Towers
Columns, beams, bracing systems and steel tower structures.
Cranes and Other Steel Structures
Lifting machinery, light steel structures and general steel construction.
SELECTION SUPPORT
TC Bolt vs. Heavy Hex Structural Bolt
Both TC bolt and Heavy Hex head Bolt are high-strength structural fasteners. Final selection depends on the approved tightening method, tool access, inspection plan, coating and project standard.
| Decision point | TC bolt assembly | Heavy hex structural bolt |
|---|---|---|
| Tightening method | Dedicated shear wrench twists off spline | Approved torque, turn-of-nut or other procedure |
| Visual indicator | Spline break-off shows completion of tool cycle | No equivalent break-off tail |
| Field productivity | Well suited to repetitive installation | Flexible conventional workflow |
| Tool access | Requires spline-socket clearance | Depends on selected tightening method |
TECHNICAL ANSWERS
Frequently Asked Questions
What components are included in one TC bolt assembly?
One high-strength TC bolt, one matching structural nut and one hardened flat washer.
Which sizes are covered by the supply range?
M16, M20, M22, M24, M27 and M30.
Which grade is most common?
The source identifies 10.9S as the common structural grade and 8.8S as a less frequently used option.
Does a broken spline alone prove acceptance?
No. It confirms completion of the tool cycle, but storage, lot condition, pre-installation verification and final inspection still matter.
Which finishes are available?
Black oxide, hot-dip galvanizing and Dacromet are listed. The approved coating must suit the project and tightening procedure.
PROJECT-SPECIFIC QUOTATION
Ready to Specify Your Tension Control Bolt Assembly?
Send the diameter, length, grade, coating, quantity and applicable project standard. Our fastening team will review the requirement and prepare a matched assembly proposal.
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