Fastener Joint Preload Estimator
Torque-preload approximation: T=KFd, so F=T/(Kd), with d converted from mm to m. A linear spring model estimates load share C=kb/(kb+kj), fastener load increase C·Q and clamp-force loss (1−C)·Q for separating load Q. Remaining clamp force is F−(1−C)·Q; a nonpositive value indicates the simplified model predicts separation. This is a screening calculation only. It omits fatigue, material strength, thread details, joint geometry, embedment, eccentricity, temperature, standards, safety factors and validation.
Simplified joint estimate
- Estimated preload
- Fastener load share
- Estimated fastener load
- Remaining clamp force
A QUICK WALKTHROUGH
How to use this tool
- Enter torque, nut factor, diameter, external load, and both stiffnesses.
- Torque, diameter and stiffnesses must be positive; K must be positive; external load must be nonnegative.
- Estimate joint loads
Model and scope
Torque-preload approximation: T=KFd, so F=T/(Kd), with d converted from mm to m. A linear spring model estimates load share C=kb/(kb+kj), fastener load increase C·Q and clamp-force loss (1−C)·Q for separating load Q. Remaining clamp force is F−(1−C)·Q; a nonpositive value indicates the simplified model predicts separation. This is a screening calculation only. It omits fatigue, material strength, thread details, joint geometry, embedment, eccentricity, temperature, standards, safety factors and validation.
Source basis and data boundary
Source basis: NASA RP-1228, simplified torque-preload and spring-stiffness load-sharing relationships. No standard tables, recommended nut factors or material properties are included; supply traceable values for the actual joint. Reference: NASA Fastener Design Manual, RP-1228: https://ntrs.nasa.gov/api/citations/19900009424/downloads/19900009424.pdf
Browser processing
Inputs and reports stay in this browser; no material properties, standards tables or default K values are bundled.
GOOD TO KNOW
Common questions
Where does K come from?
K depends on fastener, surface, coating and lubrication conditions. Supply a justified value for the actual assembly; this tool provides no default or lookup.