Tension control bolts, also known as TC bolts or twist-off bolts, are high-strength structural fasteners featuring a spline end that shears off when proper tension is achieved during installation. Designed for critical structural steel connections, they provide consistent, reliable preload with visual installation confirmation.
Applicable Standards:
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Dimensions: ASME B18.2.6 (Heavy hex structural bolts)
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Mechanical Properties: ASTM F3125/F3125M, Grade F1852, Type 1 (120 ksi minimum tensile strength)
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Thread Requirements: ASME B1.1, UNC Class 2A (bolt), Class 2B (nut)
Matching Components
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Heavy Hex Nut: ASTM A563, Grade DH (quenched and tempered carbon steel, 175 ksi proof load)
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Structural Washer: ASTM F436, Type 1 (hardened carbon steel)
Surface Finishes
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Plain finish
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Black oxide
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Hot-dip galvanized (per ASTM F2329)
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Dacromet coating
Head Marking Requirements
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Twist-Off Bolt: Manufacturer’s identification and “A325TC”
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Heavy Hex Nut: Manufacturer’s identification and “DH”
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Washer: Manufacturer’s identification
Common Applications
Steel bridges, building construction, stadiums, infrastructure projects, and other structural steel connections requiring high-strength, consistent preload
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