A structural bolt with a round head and a splined extension beyond the thread. An electric shear wrench holds the spline while turning the nut, and the reaction torque snaps the spline off at a groove when design tension is reached, leaving visible proof of installation. The result depends on the lubricant applied by the manufacturer, so TC bolts must be kept dry and installed as supplied assemblies.
Shear wrench popped every TC bolt tip, but that box sat in the rain, so pull a few for the tension calibrator before we sign off.
Also heard as
- twist-off bolt
- tension control bolt
- F1852
Do not mix it up with
- Twisted off: A twisted-off bolt is a failure; a TC bolt is designed to shear its spline off as proof of tension.
Related terms
A325
The workhorse high-strength structural bolt: heavy hex, quenched and tempered, 120 ksi minimum tensile.
DTI
Direct tension indicator: a hardened washer with bumps that flatten when the bolt reaches required tension.
Twisted off
Describes a bolt or screw that snapped in torsion while being tightened or removed, leaving the stub behind.
Preload
The tension created in a bolt by tightening it, which clamps the joint and keeps it from slipping or opening.