M20 is one of the standard coarse-thread sizes for stud bolt, double-end under GB/T 901 / DIN 939. The sections below reproduce the dimensional row, list the matching tools and hole sizes, and summarize where this size is normally specified.
M20 Dimensional Row (GB/T 901 / 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 Bolt, Double-End — GB/T 901 / DIN 939 (Series 091)
Drive geometry for M20 Stud Bolt, Double-End — GB/T 901 / DIN 939 (Series 091) 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 Bolt, Double-End — GB/T 901 / DIN 939 (Series 091) Weight
A steel M20 stud bolt, double-end 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 Bolt, Double-End — GB/T 901 / DIN 939 (Series 091)
M20 Stud Bolt, Double-End — GB/T 901 / DIN 939 (Series 091) are commonly specified for structural steelwork, heavy machinery foundations and large flange joints.
Installation Tips for M20 Stud Bolt, Double-End — GB/T 901 / DIN 939 (Series 091)
- 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.
Mating Parts for M20
For M20, pair with a M20 hex nut (ISO 4032 / DIN 934) and, where used, a M20 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.