FASTENERS & JOINTS
Estimate a bolt preload and tightening torque from proof strength, tensile stress area and nut factor.
Values are calculated locally in your browser.
Theoretical result · verify applicability below
Schematic illustration · not to scale
Nut factor is highly sensitive to friction, coating and lubrication. Torque is only an estimate, not an installation specification.
The preload target is a user-selected fraction of proof load. The empirical nut factor converts this target to approximate tightening torque. Supply the tensile stress area for the actual thread, rather than the gross circular shank area.
For d = 10 mm, At = 58 mm², Sp = 600 MPa, target fraction f = 0.7 and nut factor K = 0.2, proof load = 34.8 kN, preload = 24.36 kN and torque ≈ 48.72 N·m. All inputs are illustrative.
The initial inputs reproduce this example. Material values are illustrative inputs, not a material database or certified design values.
Single bolt, axial preload and a user-supplied nut factor. The fraction is not a universal recommendation. Friction scatter, lubrication, embedment, tool error, joint stiffness and external load sharing are excluded. Validate installation experimentally or with the applicable specification.
No factor of safety or design-code allowance is applied unless explicitly stated. Read the engineering disclaimer before applying these results.
Confirm the load direction and units first. Check the schematic against your actual supports and geometry, then compare the worked example with your own independent calculation. A valid numerical result does not establish that the model is appropriate for a real component.
For background, consult the Air Force Stress Analysis Manual’s column analysis and MIT’s Mechanics of Materials learning modules. Use applicable design standards and certified material data for real designs.