Machining
Tightening torques
In short
Torque and preload of a metric bolt by class and friction (VDI 2230), minimum preload by method. Example with the default values: Tightening torque MA = 83.6 N·m.
Calculation
Example calculated with the tool’s default values.
Inputs
- Bolt
- M12
- Property class
- 8.8
- Friction coefficient µ
- 0.12
- Yield utilisation
- 90%
- Tightening method
- Torque wrench, estimated friction (1.6–2.0)
Results
- Tightening torque MA
- 83.6 N·m
- Assembly preload FM max
- 43.1 kN
Worked example
Every value in this section belongs to the example, calculated with the tool’s default values.
Other results of the example
- Min preload FM min (αA 2,0)
- 21.6 kN
- Tensile stress at assembly
- 512 MPaRp0.2 = 640 MPa
- Bearing pressure under head
- 582 MPaCompare with the allowable pressure of the clamped part.
- Stress area As
- 84.3 mm²
- VDI 2230 friction class
- B
- Indicative values: the joint must still be checked (full VDI 2230: service loads, embedding, bearing pressure, fatigue).
Step-by-step calculation
Stress area
As = π/4 · ((d2 + d3) / 2)²
d2 10.863, d3 9.853 → 84.3 mm²
Permissible preload
FM = As · ν · Rp0.2 / √(1 + 3 [3/2 · d2/d0 · (P/(π d2) + 1.155 µ)]²)
43.11 kN
Mean bearing diameter
DKm = (dw + dh) / 2
(16.63 + 13.5) / 2 = 15.06 mm
Tightening torque
MA = FM · (0.16 P + 0.58 d2 µ + DKm/2 · µ)
83.6 N·m
Minimum preload
FM min = FM max / αA
43.11 / 2.0 = 21.55 kN
M12 8.8: by friction
| µ | FM max (kN) | MA (N·m) |
|---|---|---|
| 0.08 | 45.2 | 62.7 |
| 0.10 | 44.2 | 73.5 |
| 0.12 | 43.1 | 83.6 |
| 0.14 | 42.0 | 93.1 |
| 0.16 | 40.8 | 101.8 |
| 0.20 | 38.5 | 117.2 |
| 0.24 | 36.2 | 130.2 |
Class 8.8, µ 0,12: all sizes
| Bolt | FM max (kN) | MA (N·m) |
|---|---|---|
| M2 | 1.0 | 0.4 |
| M2.5 | 1.7 | 0.8 |
| M3 | 2.5 | 1.3 |
| M3.5 | 3.4 | 2.0 |
| M4 | 4.4 | 3.0 |
| M5 | 7.2 | 5.9 |
| M6 | 10.2 | 10.1 |
| M8 | 18.6 | 24.6 |
| M10 | 29.6 | 48.5 |
| M12 | 43.1 | 83.6 |
| M14 | 59.1 | 133.6 |
| M16 | 81.0 | 205.9 |
| M18 | 101.9 | 295.5 |
| M20 | 130.5 | 415.5 |
| M22 | 162.6 | 567.3 |
| M24 | 187.9 | 714.5 |
| M27 | 246.4 | 1050.7 |
| M30 | 300.0 | 1428.5 |
| M33 | 372.9 | 1929.7 |
| M36 | 438.1 | 2483.3 |
Friction classes (VDI 2230:2015)
| Class | µ | Examples |
|---|---|---|
| A | 0.04–0.10 | solid lubricant (MoS2, graphite, PTFE), wax |
| B | 0.08–0.16 | black oxide, phosphated, zinc plated, oiled or as delivered |
| C | 0.14–0.24 | stainless with paste, lightly oiled steel, dry zinc |
| D | 0.20–0.35 | stainless oiled, dry hot-dip galvanized |
| E | ≥ 0.30 | stainless, aluminium or Zn/Ni dry (≥ 0.30) |
Limits
Indicative results: they replace neither the applicable standards nor the job drawings and instructions. Check the values entered and the result before doing the work.
Sources
- VDI 2230 Blatt 1 : § 5.4.2 (précharge admissible à ν · Rp0,2), § 5.4.3 (couple de serrage), tableau A8 (αA)
- Bossard, Preload and tightening torques (01-2025) : p. 61–64 : FM max et MA max à 90 % de Rp0,2 (contrôle) (link)
- Bossard, Friction and friction coefficients (01-2025) : p. 57 : classes de frottement A à E (VDI 2230:2015) (link)
- ISO 4017:2022 et ISO 273:1979 : Ø d’appui dw mini ; trou de passage dh, série moyenne
- ISO 898-1, ISO 3506-1 (RoyMech) : Rp0,2 mini par classe de qualité (link)