The M20 size of General Flat Washer is dimensioned by GB/T 97.2 / ISO 7090. 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 97.2 / ISO 7090)
| For bolt size | Inner diameter d1 (mm) | Outer diameter d2 (mm) | Thickness t (mm) | Reference standard |
|---|---|---|---|---|
| M20 | 21.0 | 37.0 | 3.0 | ISO 7089 / GB/T 97.1 |
Spanner & Drive for M20 General Flat Washer — GB/T 97.2 / ISO 7090 (Series 088)
Drive geometry for M20 General Flat Washer — GB/T 97.2 / ISO 7090 (Series 088) is given by the row above; match the tool to the listed values.
Common Applications for M20 General Flat Washer — GB/T 97.2 / ISO 7090 (Series 088)
M20 General Flat Washer — GB/T 97.2 / ISO 7090 (Series 088) are commonly specified for high-load load-spreading on structural joints.
Installation Tips for M20 General Flat Washer — GB/T 97.2 / ISO 7090 (Series 088)
- 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.