Specifying Hex Flange Bolts in Grade 8.8 Steel pairs the dimensional form of Hex Flange Bolts (ISO 1665 / DIN 6921) with the engineering properties of Grade 8.8 Steel. This page explains when to choose the grade, how it behaves in service, and which grades to compare it against.
Why Choose Grade 8.8 Steel for Hex Flange Bolts
The workhorse medium-carbon alloy grade for structural joints. For hex flange bolts, 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 hex flange bolts 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 Hex Flange Bolts, 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 Hex Flange Bolts Available in Grade 8.8 Steel
| Size | Pitch (mm) | Flange diameter dc (mm) | Head height k (mm) | Width across flats s (mm) | Reference standard |
|---|---|---|---|---|---|
| M5 | 0.8 | 11.8 | 4.7 | 8.0 | ISO 1665 / DIN 6921 |
| M6 | 1.0 | 14.2 | 5.6 | 10.0 | ISO 1665 / DIN 6921 |
| M8 | 1.25 | 17.9 | 7.2 | 13.0 | ISO 1665 / DIN 6921 |
| M10 | 1.5 | 21.8 | 8.9 | 15.0 | ISO 1665 / DIN 6921 |
| M12 | 1.75 | 26.0 | 10.7 | 18.0 | ISO 1665 / DIN 6921 |
| M14 | 2.0 | 29.9 | 12.3 | 21.0 | ISO 1665 / DIN 6921 |
| M16 | 2.0 | 34.5 | 14.1 | 24.0 | ISO 1665 / DIN 6921 |
| M20 | 2.5 | 42.8 | 17.5 | 30.0 | ISO 1665 / DIN 6921 |
| M24 | 3.0 | 51.1 | 21.0 | 36.0 | ISO 1665 / DIN 6921 |