For button head socket screws in Grade 8.8 Steel, the controlling selection factors are corrosion exposure, strength requirement and service temperature. The grade data for Grade 8.8 Steel (class 8.8) is summarized below together with every size supplied.
Why Choose Grade 8.8 Steel for Button Head Socket Screws
The workhorse medium-carbon alloy grade for structural joints. For button head socket screws, 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 |
Corrosion Behavior in Service
Carbon and alloy steel button head socket screws require a coating for corrosion protection. Zinc plating (with or without passivation) is the most common; hot-dip galvanizing is used for outdoor structural service; black-oxide is mainly a tarnish-prevention finish for tool-room use.
Galvanic & Galling Considerations
For button head socket screws 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.
Sizes of Button Head Socket Screws Available in Grade 8.8 Steel
| Size | Pitch (mm) | Head diameter dk (mm) | Head height k (mm) | Hex socket s (mm) | Reference standard |
|---|---|---|---|---|---|
| M3 | 0.5 | 5.7 | 1.65 | 2.0 | ISO 7380-1 / DIN 7380 |
| M4 | 0.7 | 7.6 | 2.2 | 2.5 | ISO 7380-1 / DIN 7380 |
| M5 | 0.8 | 9.5 | 2.75 | 3.0 | ISO 7380-1 / DIN 7380 |
| M6 | 1.0 | 10.5 | 3.3 | 4.0 | ISO 7380-1 / DIN 7380 |
| M8 | 1.25 | 14.0 | 4.4 | 5.0 | ISO 7380-1 / DIN 7380 |
| M10 | 1.5 | 17.5 | 5.5 | 6.0 | ISO 7380-1 / DIN 7380 |
| M12 | 1.75 | 21.0 | 6.6 | 8.0 | ISO 7380-1 / DIN 7380 |
| M14 | 2.0 | 24.5 | 7.7 | 10.0 | ISO 7380-1 / DIN 7380 |
| M16 | 2.0 | 28.0 | 8.8 | 10.0 | ISO 7380-1 / DIN 7380 |
| M20 | 2.5 | 35.0 | 11.0 | 12.0 | ISO 7380-1 / DIN 7380 |