Formula: T = K × d × FV |
FV = As × Rp0.2 × utilization
K = nut factor (torque coefficient) | d = nominal diameter (mm) |
As = tensile stress area (mm²)
Tightening torques — 8.8, K = 0.15, utilization 90 %
Size
Pitch (mm)
As (mm²)
FV (kN)
Torque (Nm)
Notes
Strength class marking: first digit × 100 = tensile strength (MPa), first digit × last digit × 10 = yield strength (MPa).
Example: 8.8 → Rm = 800 MPa, Rp0.2 = 640 MPa.
Friction coefficient K: value depends on surface finish, coating, and lubricant.
Unlubricated as-supplied bolts: K ≈ 0.20. Always use consistent lubricant for critical joints.
Utilization: 90% is standard for controlled torque tightening. Yield-controlled tightening (100%) requires angle monitoring.