Property Class 8.8 Steel Tension-Control Structural Bolt Assemblies (TC / Twist-Off) are supplied to ISO 898-1 property class 8.8. Corrosion behaviour is requires plating (zinc) for corrosion protection, the material is magnetic, and the usable service range is commonly limited to approx. +300 °C; confirm against the coating and the load. In practice this grade is the workhorse medium-carbon alloy class for structural joints.
- Grade
- ISO 898-1 property class 8.8
- Corrosion resistance
- Requires plating (zinc) for corrosion protection
- Magnetic response
- Magnetic
- Service temperature
- commonly limited to approx. +300 °C; confirm against the coating and the load
Property values are typical for the grade. Certified mechanical test data is available on request for production orders.
Property Class 8.8 Steel Tension-Control Structural Bolt Assemblies (TC / Twist-Off) are supplied to ASTM F3125/F3125M Grade F1852 and F2280. The grade provides requires plating (zinc) for corrosion protection and is magnetic; the practical service range is commonly limited to approx. +300 °C; confirm against the coating and the load. Property data, grade comparison and the full size table follow.
Why Choose Property Class 8.8 Steel for Tension-Control Structural Bolt Assemblies (TC / Twist-Off)
The workhorse medium-carbon alloy class for structural joints. For tension-control structural bolt assemblies (tc / twist-off), this matters when requires plating (zinc) for corrosion protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 898-1 property class 8.8 |
|---|
| Magnetic response | Magnetic |
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| Service temperature | commonly limited to approx. +300 °C; confirm against the coating and the load |
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| Corrosion characteristic | Requires plating (zinc) for corrosion protection |
|---|
Corrosion Behavior in Service
Carbon and alloy steel tension-control structural bolt assemblies (tc / twist-off) require a coating for corrosion protection. Zinc plating (with or without passivation) is the most common; hot-dip galvanizing is used for outdoor structural service; black-oxide is mainly a tarnish-prevention finish for tool-room use.
Galvanic & Galling Considerations
For tension-control structural bolt assemblies (tc / twist-off) in steel, the dominant compatibility issue is hydrogen embrittlement at high property classes (10.9 and above) when electroplated. Plating must be followed by an appropriate baking treatment, or a non-electroplated finish (mechanical zinc, zinc flake) should be substituted.
Sizes of Tension-Control Structural Bolt Assemblies (TC / Twist-Off) Available in Property Class 8.8 Steel
| Size | Thread series | Assembly | Minimum installation tension F1852 (lbf) | Minimum installation tension F2280 (lbf) | Finish | Reference standard |
|---|
| 1/2-13 | UNC | bolt + twist-off nut + washer | 12,550 | 15,650 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| 5/8-11 | UNC | bolt + twist-off nut + washer | 19,900 | 24,900 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| 3/4-10 | UNC | bolt + twist-off nut + washer | 29,450 | 36,800 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| 7/8-9 | UNC | bolt + twist-off nut + washer | 40,750 | 50,950 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| 1-8 | UNC | bolt + twist-off nut + washer | 53,450 | 66,800 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| 1-1/8-7 | UNC | bolt + twist-off nut + washer | 67,350 | 84,100 | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| M16 | Metric option | bolt + twist-off nut + washer | | | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
| M20 | Metric option | bolt + twist-off nut + washer | | | Plain, heat-treated alloy steel | ASTM F3125/F3125M Grade F1852 and F2280 |
Applications & Industries
Tension-Control Structural Bolt Assemblies are bought for a small number of well-defined jobs. These are the ones we ship them for. Stocked from 1/2-13 to M20 (screw size).
Industries that specify Tension-Control Structural Bolt Assemblies
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Industrial fabrication
One-pass structural assembly where repeatable tension matters more than later disassembly.
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Steel erection
Matched structural bolt assemblies tensioned in beam, column and splice connections.
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Bridge construction
Slip-critical steel joints where the final tension is set by the twist-off installation system.
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Heavy transport
Truck frames and chassis joints exposed to road vibration and cyclic load.
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Food, pharma & cleanroom
Stainless assemblies that are washed down, where the finish matters as much as the strength.
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Machine building & OEM
The default fastener on production equipment: covers, brackets, motor mounts and sub-assemblies tightened to a specified torque.
Typical applications
- using the plain shank and heavy hex geometry for steel-to-steel joints
- installing a matched bolt, nut and washer assembly with a controlled twist-off spline
- setting structural tension without a separate torque reaction wrench on the nut
- selecting F1852 or F2280 together with the required installation tension
- joints where the property class is stated on the drawing
- clamping two machined faces to a calculated preload
Service conditions to specify against
- Marine and coastal
- Available in A4 (316) stainless for chloride exposure — coastal structures, pool halls, water treatment and deck hardware, where A2 will eventually pit.
- High load
- Supplied in ISO 898-1 property classes, so the joint can be designed to a stated proof load and tightened to a calculated torque rather than by feel.
- Torque and preload
- The joint is designed around bolt tension, so lubrication, coating and the friction coefficient all change the torque figure — state them together.
Where to use something else
- Do not reuse the twisted-off spline or substitute a generic torque value for the grade-specific installation method.
- Do not use a machine thread into unthreaded sheet or timber; use a tapping screw, rivet nut or insert made for that parent material.
Full application guide: where Tension-Control Structural Bolt Assemblies are used, how to specify them, and the cases they are wrong for
