Calculate tightening torque from target preload, with thread engagement analysis and material warnings
Bolt Selection
in
ksi
ksi
Thread Condition
%
Joint Configuration
🔩 Bolt + Nut
🔧 Bolt into Threaded Part
in
ksi
Results
Torque (ft·lb)
—
Torque (N·m)
—
Torque (lb·in)
—
Preload (lb)
—
Preload (kN)
—
Proof Load (lb)
—
Bolt Size
—
Tensile Stress Area
—
K Factor Used
—
Thread Shear Capacity
—
Thread Safety Factor
—
Important Notes
Torque ≠ Preload: Torque is an indirect method to achieve preload. Up to 90% of applied torque is absorbed by friction — only ~10% stretches the bolt. Actual preload varies ±25-30% with torque wrenches.
K Factor is critical: The same torque produces vastly different preloads depending on lubrication. Always verify your thread condition matches the K factor used.
Thread engagement: For steel bolts into aluminum, minimum 2×d engagement (or 1.5×d with thread inserts). The first 2-3 threads carry ~90% of the load — additional length provides safety margin, not proportional strength.
For critical applications: Consider direct preload measurement (bolt stretch, ultrasonic, or load-indicating washers) instead of torque.