The M20 size of Stud is dimensioned by GB/T 15389 / DIN 939. The tables below give the dimensional row from the standard, the drill and spanner sizes that go with it, and the assembly torque per property class. The technical drawing on this page redraws to the exact values selected.
M20 Dimensional Row (GB/T 15389 / DIN 939)
| Thread size | Pitch (mm) | Length L (mm) | Engagement depth bm (mm) | Material | Reference standard |
|---|---|---|---|---|---|
| M20 | 2.5 | 180 | 30 | Cl. 8.8 alloy steel | DIN 939 / GB/T 901 |
Spanner & Drive for M20 Stud — GB/T 15389 / DIN 939 (Series 096)
Drive geometry for M20 Stud — GB/T 15389 / DIN 939 (Series 096) is given by the row above; match the tool to the listed values.
Hole Sizes for M20
| Coarse-thread pitch (ISO 724) | 2.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 22 mm |
| Tapping drill, coarse thread | 17.5 mm |
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.
M20 Stud — GB/T 15389 / DIN 939 (Series 096) Weight
A steel M20 stud at the listed 180 mm length weighs approximately 444 g each — about 444 kg per 1,000 pieces. Stainless A2/A4 weighs roughly the same (density 7.9–8.0 g/cm³). Actual weight varies slightly with head form, thread and finish; use this figure for freight estimation only.
Common Applications for M20 Stud — GB/T 15389 / DIN 939 (Series 096)
M20 Stud — GB/T 15389 / DIN 939 (Series 096) are commonly specified for structural steelwork, heavy machinery foundations and large flange joints.
Installation Tips for M20 Stud — GB/T 15389 / DIN 939 (Series 096)
- 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.