Dimensional and assembly data for M20 Flat Washers to ISO 7089 / ISO 7093. Includes head size and width across flats, clearance-hole and tapping-drill diameters, tightening torque per property class, and the sizes to step up or down to when the joint requires it.
M20 Dimensional Row (ISO 7089 / ISO 7093)
| For bolt size | Inner diameter d1 min (mm) | Outer diameter d2 max (mm) | Thickness h (mm) | Reference standard |
|---|---|---|---|---|
| M20 | 21.0 | 37.0 | 3.0 | ISO 7089 |
Spanner & Drive for M20 Flat Washers
Drive geometry for M20 Flat Washers is given by the row above; match the tool to the listed values.
Common Applications for M20 Flat Washers
M20 Flat Washers are commonly specified for high-load load-spreading on structural joints.
Installation Tips for M20 Flat Washers
- 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.