How to find the right Tension Control Bolts AI guide
Written by an AI model from its trained knowledge.
What the AI looks for in Tension Control Bolts
- Specification grade
- Order to ASTM F3125, using Grade F1852 (A325-level strength) or Grade F2280 (A490-level strength), exactly as the structural drawings specify. The engineer of record sets the strength level, and the two grades are not interchangeable.
- Matched assembly lot
- Buy the bolt, nut and washer as a manufacturer-supplied assembly from one lot. Twist-off tension depends on lubrication and thread condition, which the maker controls as a set.
- Pre-installation verification
- Test a sample from each lot in a bolt tension calibrator before use, per the RCSC Specification. This confirms the spline actually breaks off at or above the required pretension.
- Coating
- Use plain or weathering (Type 3) bolts as specified. Never use hot-dip galvanized A490-level (F2280) bolts. Galvanizing high-strength bolts risks hydrogen embrittlement, and the coating changes the torque-tension behavior.
- Storage and condition
- Keep bolts sealed and dry until installation. Do not use rusty or washed-out assemblies, and do not reuse installed bolts. Lost lubricant raises friction, so the spline snaps before the bolt reaches proper tension.
- Installation tool
- Install with a shear wrench sized to the bolt diameter, after snugging the joint first. The tool reacts against the spline, and an unsnugged joint gives false completion.
Brands that matter
- LeJeune Bolt: US structural bolt maker well known for twist-off tension control bolts.
- Nucor Fastener: Major US producer of structural bolting assemblies.
- St. Louis Screw & Bolt: US structural bolt manufacturer that supplies TC assemblies.
What to avoid
- Mixing nuts or washers from other lots or makers into TC assemblies.
- Hot-dip galvanized A490-level tension control bolts.
- Weathered or wet assemblies left uncovered on site.
- Using a sheared spline as proof of tension without lot verification.
Questions
Can a tension control bolt be reused after the spline snaps?
No. It is single-use, and once installed to pretension it must be replaced if removed.
Do I need TC bolts instead of regular structural hex bolts?
Only when the joint is pretensioned or slip-critical. TC bolts are one approved way to reach pretension; turn-of-nut and direct tension indicators are others.