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Bolted Joint Torque Calculator_
Calculate proper tightening torque for bolted joints based on material and preload requirements
Thread Size
Sets diameter and pitch. Strength is a property of the class, not the size, so pick it separately below.
Bolt Parameters
Class 8.8: 800 MPa minimum tensile, 640 MPa yield, 580 MPa proof.
The class designation states the strength: 8.8 is 800 MPa tensile and 640 MPa yield, 10.9 is 1000 MPa nominal. Editing this switches to a custom material.
Dry steel = 0.2, Lubricated = 0.15
Typical: 60-80%
Required Torque
0.0
N·m
Target Preload Force
0.00 kN
0 N
Bolt Stress
0.0 MPa
0.0% of tensile strength
0.0% of proof stress
Stress Area
0.0 mm²
Tensile stress area, ISO 898-1
Usage Notes
- • Torque: T = K × D × F (Coefficient × Diameter × Preload Force)
- • Stress area: As = (π/4) × (d − 0.9382 × P)², ISO 898-1
- • K factor varies with lubrication (dry ≈ 0.20, lubricated ≈ 0.15, anti-seize ≈ 0.10)
- • Preload here is a percentage of tensile strength divided by the safety factor. The proof ratio is shown alongside it because proof stress is the usual reference for a reusable joint.
- • Property class values are ISO 898-1. Class 8.8 takes higher minima above M16, which this tool applies automatically.
What this tool does not account for
- • Joint stiffness, gasket relaxation, embedding and any external service load. This is bolt capacity, not a joint analysis.
- • Thread engagement length, or whether the tapped material can carry the preload. A bolt can be stronger than the thread it goes into.
- • Temperature, fatigue, prevailing torque from locking features, and coating effects on K. The nut factor is an estimate with real scatter.
- • Manufacturer torque specifications always take precedence, and this tool is an estimate rather than a verification. Have critical joints checked by a qualified engineer.