Calculator
Install torque to reach a target preload. Pick a size and proof strength, set the nut factor K, and read the recommended and maximum torque and the resulting bolt tension.
Tightening a bolt converts applied torque into preload (clamp force). The short-form relationship is T = K · d · F, where K is the nut factor, a single empirical number that lumps together thread friction, bearing friction, and geometry. Because friction scatters from part to part, the achieved preload for a given torque typically varies ±25–35%, which is why this is a preliminary tool.
The target preload is taken as a fraction of the bolt's proof load Fp = Sp · At: recommended = 0.75·Fp (reused / non-permanent joints) and maximum = 0.90·Fp (near-proof, permanent joints). These are the Shigley / Machinery's Handbook recommended preload values (0.75·Fp reused, 0.90·Fp permanent). They are conventional design points; a future revision will make the factor user-adjustable for your application.
Standards used:ASME B1.1 (tensile stress area), Shigley & Machinery's Handbook (proof load and nut factor K). Material strength presets are first-pass handbook values flagged for review; auto-filled but editable.
Preliminary / convenience use only. Verify all values against your governing material spec and standard before design release.
Editable; auto-filled from Size.
Auto-fills Proof Strength; editable. Custom clears it.
Bolt proof strength. Required to compute.
External axial load on the joint (default 0).
Advanced users only; K depends on lubrication / coating. Common: 0.30 nonplated, 0.20 zinc, 0.18 lubricated, 0.12 anti-seize.
Auto-fills the coefficient of friction μ; editable. Optional, drives the slip check.
Sliding friction between the clamped surfaces. NOT the same as K (nut factor).
Brackets the nominal preload into a min / max range.
Tightening scatter in the achieved preload. Standard value: 25%.
Long-term preload loss (embedment / creep). Standard value: 10%.
Length of thread engagement in the receptacle.
Auto-fills Yield Strength; editable. Custom clears it.
Receptacle material yield strength.
bolt torque · torque · preload · clamp force · nut factor · K factor · proof strength · tensile stress area · fastener · install torque · tightening · ASME B1.1