The M20 size of Hexagon Coupling Nuts is dimensioned by DIN 6334. The table below gives the dimensional row from the standard, followed by the drive and the installation notes for this type.
M20 Dimensional Row (DIN 6334)
| Size | Pitch (mm) | Width across flats s (mm) | Width across corners e (mm) | Length l (mm) | Reference standard |
|---|---|---|---|---|---|
| M20 | 2.5 | 30 | 33.53 | 60 | DIN 6334 |
Spanner & Drive for M20 Hexagon Coupling Nuts
Drive geometry for M20 Hexagon Coupling Nuts is given by the row above; match the tool to the listed values.
Tightening Torque for M20
| Class 8.8 (dry, ~µ 0.125) | ≈ 410 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 580 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 690 Nm |
Indicative dry-joint values. Lubrication can lower the required torque by 15–25%. Always confirm against the joint design, especially when going up a strength class.
Proof Load & Strength for M20
| Tensile stress area As (ISO 898-1) | 245 mm² |
|---|---|
| Proof load, class 8.8 | 147 kN |
| Proof load, class 10.9 | 203 kN |
| Proof load, class 12.9 | 238 kN |
| Min. ultimate tensile, class 8.8 | 196 kN |
Proof load = stress area × proof stress per ISO 898-1. Design joints so the working preload stays below the proof load of the selected class.
Common Applications for M20 Hexagon Coupling Nuts
M20 Hexagon Coupling Nuts are commonly specified for structural joints, flange connections and heavy equipment foundations.
Installation Tips for M20 Hexagon Coupling Nuts
- At M20 the stretch in the bolt becomes the controlling factor — for critical joints, use angle-controlled or stretch-controlled tightening instead of pure torque.
When to Step Up or Down from M20
When the joint preload approaches the proof load of M20 class 8.8, step up to M24 class 8.8 (or move to M20 class 10.9). When the joint is over-specified, M16 often saves weight and cost without losing the safety margin.
