Property Class 8.8 Steel Tension-Control Structural Bolt Assemblies (TC / Twist-Off)

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

• Industrial fabrication One-pass structural assembly where repeatable tension matters more than later disassembly.
• Steel erection Matched structural bolt assemblies tensioned in beam, column and splice connections.
• Bridge construction Slip-critical steel joints where the final tension is set by the twist-off installation system.
• Heavy transport Truck frames and chassis joints exposed to road vibration and cyclic load.
• Food, pharma & cleanroom Stainless assemblies that are washed down, where the finish matters as much as the strength.
• 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