Tension control bolts, often referred to as TC bolts or twist-off bolts, are high-strength fasteners covered under the ASTM F3125 specification for structural bolts. They are manufactured in two grades:
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ASTM F1852 – equivalent in strength to A325 structural bolts.
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ASTM F2280 – equivalent in strength to A490 structural bolts.
These bolts are widely used in bridges, steel buildings, stadiums, and other infrastructure projects where high-strength, consistent connections are essential. These high-strength fasteners are available in both plain finish and hot-dip galvanized to meet your requirements.
TC Bolts Installation
TC bolts feature a spline that shears off when the proper tension is achieved. Using a specialized shear wrench, the bolt automatically tightens until the spline twists off, providing a clear visual indication that the correct preload has been reached. This system:
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Eliminates guesswork from torque-based tightening.
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Improves installation speed and consistency.
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Ensures reliable performance in critical structural steel connections.
Advantages of TC Bolts
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Consistent tensioning: Accurate and repeatable preload on every installation.
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Faster installation: Reduced labor time compared to calibrated wrench methods.
Mechanical Properties of TC Bolts
The mechanical properties of tension control bolts are those identified in the ASTM F3125 specification, as this is the specification that covers tension control bolts.
| Grade | Tensile, ksi | Yield, ksi min | Elongation, % min | RA, % min |
|---|---|---|---|---|
| 120ksi (A325/F1852) | 120 min | 92 | 14 | 35 |
| 150ksi (A490/F2280) | 150-173 | 130 | 14 | 40 |
Permitted Coatings of TC Bolts
Permitted coatings for tension control bolts are also outlined in the specification ASTM F3125, as the following chart indicates.
| Bolt | F2329 Hot Dip Galvanizing | B695 Mechanical Galvanizing | F1136 Zinc/Aluminum (Geomet) | F2833 Zinc/Aluminum |
|---|---|---|---|---|
| A325 | Approved | Class 55 | Grade 3 | Grade 1 |
| F1852 | Not Approved | Class 55 | Not Approved | Not Approved |
| A490 | Not Approved | Not Approved | Grade 3 | Grade 1 |
| F2280 | Not Approved | Not Approved | Not Approved | Not Approved |
| *Other coatings may be used on 120ksi/A325 fasteners upon agreement between purchaser and user. Coatings on 150ksi/A490 fasteners must be qualified by ASTM committee F16.
*F1136, F2833 and F3019, as of 2020, have been withdrawn and combined into a new coating standard, F3393. | ||||
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