Grade 12.9 Steel Sheet-Metal Self-Tapping Screw combine the dimensional form of GB/T 845 / ISO 7049 with the material properties of grade class 12.9: requires plating or black-oxide protection, magnetic, service range up to approx. +300 °C. This page summarizes the grade data, its corrosion behavior in service, the comparable grades, and the sizes supplied.
Why Choose Grade 12.9 Steel for Sheet-Metal Self-Tapping Screw — GB/T 845 / ISO 7049 (Series 045)
The highest common strength class, for high-load machine assembly. For sheet-metal self-tapping screw — gb/t 845 / iso 7049 (series 045), this matters when requires plating or black-oxide protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | class 12.9 |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | up to approx. +300 °C |
| Corrosion characteristic | Requires plating or black-oxide protection |
Galvanic & Galling Considerations
For sheet-metal self-tapping screw — gb/t 845 / iso 7049 (series 045) 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 Sheet-Metal Self-Tapping Screw — GB/T 845 / ISO 7049 (Series 045), class 8.8 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 Sheet-Metal Self-Tapping Screw — GB/T 845 / ISO 7049 (Series 045) Available in Grade 12.9 Steel
| Size | Nominal diameter (mm) | Pitch (mm) | Length L (mm) | Head diameter dk (mm) | Head height k (mm) | Reference standard |
|---|---|---|---|---|---|---|
| ST2.2 | 2.2 | 0.8 | 9.5 | 4.2 | 1.4 | ISO 1481 / GB/T 845 |
| ST2.9 | 2.9 | 1.1 | 13 | 5.6 | 1.7 | ISO 1481 / GB/T 845 |
| ST3.5 | 3.5 | 1.3 | 16 | 6.9 | 2.1 | ISO 1481 / GB/T 845 |
| ST3.9 | 3.9 | 1.3 | 16 | 7.5 | 2.3 | ISO 1481 / GB/T 845 |
| ST4.2 | 4.2 | 1.4 | 19 | 8.2 | 2.5 | ISO 1481 / GB/T 845 |
| ST4.8 | 4.8 | 1.6 | 25 | 9.5 | 2.9 | ISO 1481 / GB/T 845 |
| ST5.5 | 5.5 | 1.8 | 32 | 10.9 | 3.3 | ISO 1481 / GB/T 845 |
| ST6.3 | 6.3 | 1.8 | 38 | 12.5 | 3.8 | ISO 1481 / GB/T 845 |