By Zencalcy Editorial TeamLast reviewed About us
Torque is how you create preload, and preload is what keeps a joint from separating. The short form is T = K × d × F, where K bundles thread and under-head friction: about 0.20 dry, 0.16 lubricated and 0.28 for zinc plating.
Tightening torque for a preloaded bolt.
T = K × d × F
T is torque, d is nominal diameter, F is preload and K is the nut factor. A common target preload is 60–75% of proof load; for a grade 5 bolt that is roughly 12,000 lb per square inch of tensile area. Always use the fastener manufacturer's value when one exists.
| Symbol | Meaning |
|---|---|
| K | Nut factor (friction). |
| d | Nominal bolt diameter. |
| F | Preload / clamp force. |
T = 0.20 × 0.5 × 8,000 = 800 lb·in, or 66.7 lb·ft (90 N·m).
Continue with the Beam Deflection Calculator, Beam Load Calculator, Bending Stress Calculator, or the Wood Beam Span Calculator — or browse more structural & workshop and all construction calculators.
An empirical number that lumps thread friction and under-head friction. It varies with lubrication, plating and surface finish.
Results use standard construction estimating arithmetic: volumes from measured area and depth, unit weights from published material densities, and code-referenced spans or clearances where the page names a code. Quantities are rounded up to whole saleable units and include the stated waste allowance. These tools are planning aids, not structural design, and do not replace a licensed engineer, a local code check, or a contractor's site measurement.
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Content updated: September 2026