Maximum Tightening Torque Calculator
Maximum tightening torque for a target equivalent stress (Von Mises) at yield.
Section A
User inputs
Dry: 0.14–0.20 · Oiled: 0.08–0.14 · MoS2: 0.04–0.08
Usually equal to or slightly higher than μthread
Section B
Thread & material parameters (ISO 724)
| Thread geometry | |
|---|---|
| Nominal diameter d | — |
| Pitch P | — |
| Pitch diameter d2 | — |
| Root diameter d3 | — |
| Mean stress dia. dm | — |
| Tensile stress area At | — |
| At calc. check (π/4·dm²) | — |
| Material properties & stress goals | |
|---|---|
| Strength class | — |
| Ultimate tensile str. Rm | — |
| Yield strength Rp0.2 | — |
| Target σe fraction | — |
| Tensile stress σt | — |
| Thread friction μthread | — |
| Head friction μhead | — |
Key results
Tightening torque (MA = MG + MWD)
—
Initial preload (Fi = σt × At)
—
Load at yield (F0.2 = Rp0.2 × At)
—
Load reserve (Pb = F0.2 − Fi)
—
Von Mises equiv. stress (σe = √(σt² + 3τ²))
—
Section C
Stress & torque breakdown
| Parameter | Value | Unit | Notes / formula |
|---|---|---|---|
| Thread friction torque MG (tighten) | — | N·m | Tightening direction |
| Thread friction torque MG (loosen) | — | N·m | Loosening direction |
| Head/face friction torque MWD | — | N·m | MWD = Fi × μhead × 1.3 × d/2 |
| Total tightening torque MA | — | N·m | MA = MG + MWD |
| Torsional stress τ | — | MPa | τ = MG / (π/16 × d3³) — relaxes after tightening |
| Tensile stress σt | — | MPa | Solved for target σe |
| Von Mises equiv. stress σe | — | MPa | σe = √(σt² + 3τ²) |
| Stress relaxation | — | % | (σe − σt) / σe |
| Yield strength Rp0.2 | — | MPa | F0.2 = Rp0.2 × At |
Utilisation σe / Rp0.2 = —
(1) Equivalent stress combines tension and torsion during tightening.
(2) Stress relaxation: (σe − σt) / σe — torsional share that fades after setting.
(3) Tightening to yield: target σe = Rp0.2 at 100%.