Grade 8.8 Steel (class 8.8) is the workhorse medium-carbon alloy grade for structural joints. When flat washers are specified in this grade, the dimensions remain per ISO 7089 / ISO 7093; the material determines corrosion behavior (requires plating (zinc) for corrosion protection) and the service temperature range (up to approx. +300 °C). Both are covered below with the size table.
Why Choose Grade 8.8 Steel for Flat Washers
The workhorse medium-carbon alloy grade for structural joints. For flat washers, this matters when requires plating (zinc) for corrosion protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | class 8.8 |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | up to approx. +300 °C |
| Corrosion characteristic | Requires plating (zinc) for corrosion protection |
Galvanic & Galling Considerations
For flat washers in steel, the dominant compatibility issue is hydrogen embrittlement at high property classes (10.9 and above) when electroplated. Plating must be followed by an appropriate baking treatment, or a non-electroplated finish (mechanical zinc, zinc flake) should be substituted.
Comparable Grades
For Flat Washers, class 10.9 or 12.9 is the comparable strength step. Move up when the joint preload approaches the proof load of the current class; move down when the joint is over-specified. For corrosion-critical service, switch to stainless A2 or A4.
Sizes of Flat Washers Available in Grade 8.8 Steel
| For bolt size | Inner diameter d1 min (mm) | Outer diameter d2 max (mm) | Thickness h (mm) | Reference standard |
|---|---|---|---|---|
| M1.6 | 1.7 | 4.0 | 0.3 | ISO 7089 |
| M2 | 2.2 | 5.0 | 0.3 | ISO 7089 |
| M2.5 | 2.7 | 6.0 | 0.5 | ISO 7089 |
| M3 | 3.2 | 7.0 | 0.5 | ISO 7089 |
| M3.5 | 3.7 | 8.0 | 0.5 | ISO 7089 |
| M4 | 4.3 | 9.0 | 0.8 | ISO 7089 |
| M5 | 5.3 | 10.0 | 1.0 | ISO 7089 |
| M6 | 6.4 | 12.0 | 1.6 | ISO 7089 |
| M7 | 7.4 | 14.0 | 1.6 | ISO 7089 |
| M8 | 8.4 | 16.0 | 1.6 | ISO 7089 |
| M10 | 10.5 | 20.0 | 2.0 | ISO 7089 |
| M12 | 13.0 | 24.0 | 2.5 | ISO 7089 |
| M14 | 15.0 | 28.0 | 2.5 | ISO 7089 |
| M16 | 17.0 | 30.0 | 3.0 | ISO 7089 |
| M18 | 19.0 | 34.0 | 3.0 | ISO 7089 |
| M20 | 21.0 | 37.0 | 3.0 | ISO 7089 |
| M22 | 23.0 | 39.0 | 3.0 | ISO 7089 |
| M24 | 25.0 | 44.0 | 4.0 | ISO 7089 |
| M27 | 28.0 | 50.0 | 4.0 | ISO 7089 |
| M30 | 31.0 | 56.0 | 4.0 | ISO 7089 |
| M33 | 34.0 | 60.0 | 5.0 | ISO 7089 |
| M36 | 37.0 | 66.0 | 5.0 | ISO 7089 |
| M39 | 40.0 | 72.0 | 6.0 | ISO 7089 |
| M42 | 43.0 | 78.0 | 7.0 | ISO 7089 |
| M45 | 46.0 | 85.0 | 7.0 | ISO 7089 |
| M48 | 50.0 | 92.0 | 8.0 | ISO 7089 |
| M52 | 54.0 | 98.0 | 8.0 | ISO 7089 |
| M56 | 58.0 | 105.0 | 9.0 | ISO 7089 |
| M60 | 62.0 | 110.0 | 9.0 | ISO 7089 |
| M64 | 66.0 | 115.0 | 9.0 | ISO 7089 |