Determine bolt preload from tightening torque, thread geometry, and separate friction conditions.
Set the inputs and start the calculation.
Derive achievable assembly preload from torque, thread geometry and friction.
Tightening torque, nominal diameter, pitch, friction coefficients and tightening factor are required; property class limits allowable preload.
Target preload must preserve clamp force while staying below proof and yield limits. Pitch and friction split the torque; scatter is represented by the tightening factor.
Invert the torque equation to obtain preload. Thread and bearing friction consume most of the applied torque.
Doubling friction can strongly reduce calculated preload at unchanged torque.
Sources and limits: ISO 16047 and VDI 2230; check allowable assembly preload against ISO 898-1 and supplier data.
Derive achievable assembly preload from torque, thread geometry and friction.
Bolt calculations describe a joint through geometry, preload, friction and material limits. Preload clamps the parts; external load, embedding and temperature change the reserve.
Invert the torque equation to obtain preload. Thread and bearing friction consume most of the applied torque.
Tightening torque, nominal diameter, pitch, friction coefficients and tightening factor are required; property class limits allowable preload. Target preload must preserve clamp force while staying below proof and yield limits. Pitch and friction split the torque; scatter is represented by the tightening factor.
Enter the intended or measured tightening torque, thread nominal diameter and pitch, and thread/bearing friction coefficients. Compare the resulting preload against the allowable assembly preload for the property class.
Doubling friction can strongly reduce calculated preload at unchanged torque.
Target preload must preserve clamp force while staying below proof and yield limits. Pitch and friction split the torque; scatter is represented by the tightening factor. A passing result means only that the selected model stays within the entered limits. Tightening scatter and real contact surfaces may govern residual clamp force.
Torque in N·m, diameter and pitch in mm, friction coefficients dimensionless, result in kN.
Estimating the preload achieved at a given assembly torque, or checking whether a workshop-standard torque for the specific bolt size produces sufficient clamp force at all.
ISO 16047 and VDI 2230; check allowable assembly preload against ISO 898-1 and supplier data.
Common mistake: Don't treat the result as an exact value – it is an estimate from assumed friction coefficients. Also check the result against the property class's allowable assembly preload, since torque-controlled tightening at too high a torque can plastically stretch the bolt.
Because friction consumes most of the torque and can scatter 20 to 30% even with careful assembly; only angle- or elongation-controlled tightening substantially reduces this scatter.
It accounts for the scatter of the chosen tightening method (e.g. impact wrench versus torque-controlled wrench) when setting allowable assembly preload.
It follows from tensile stress area Aₛ and a fraction of yield or minimum tensile stress per ISO 898-1, typically 70 to 90% depending on tightening method and safety requirement.
Tightening torque, thread size, bearing diameter, and friction coefficients estimate assembly preload.
The calculator inverts the same friction model as the torque calculator. It reveals how assumed friction shifts expected preload, but it does not replace measurement.
Without tested friction data, actual preload is much less certain than the display suggests.
For critical joints, consider direct or indirect preload measurement or monitored tightening.
Preload immediately after assembly is not automatically the minimum clamp load retained in service.
Determines actual torque/preload behaviour under defined test conditions.
Assesses tightening factor, embedding, and required minimum preload.
Extends single-bolt principles to multi-bolt joints.