Grade 12.9 Steel Shoulder Bolts pairs the standard ISO 7379 with a Grade 12.9 Steel base material. The sections below cover why engineers select this grade for shoulder bolts, its corrosion and temperature behavior, and the sizes available.
Why Choose Grade 12.9 Steel for Shoulder Bolts
The highest common strength class, for high-load machine assembly. For shoulder bolts, 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 shoulder 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 Shoulder Bolts, 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 Shoulder Bolts Available in Grade 12.9 Steel
| Shoulder diameter (mm) | Thread size | Pitch (mm) | Shoulder length range (mm) | Head diameter dk (mm) | Head height k (mm) | Reference standard |
|---|---|---|---|---|---|---|
| 4.0 | M3 | 0.5 | 8~50 | 8.0 | 4.3 | ISO 7379 / DIN 9841 |
| 5.0 | M4 | 0.7 | 8~63 | 9.5 | 5.3 | ISO 7379 / DIN 9841 |
| 6.0 | M5 | 0.8 | 10~63 | 11.0 | 6.5 | ISO 7379 / DIN 9841 |
| 8.0 | M6 | 1.0 | 10~80 | 13.0 | 8.0 | ISO 7379 / DIN 9841 |
| 10.0 | M8 | 1.25 | 12~100 | 16.0 | 10.0 | ISO 7379 / DIN 9841 |
| 12.0 | M10 | 1.5 | 16~100 | 18.0 | 12.0 | ISO 7379 / DIN 9841 |
| 16.0 | M12 | 1.75 | 20~125 | 24.0 | 16.0 | ISO 7379 / DIN 9841 |
| 20.0 | M16 | 2.0 | 25~160 | 30.0 | 20.0 | ISO 7379 / DIN 9841 |
| 25.0 | M20 | 2.5 | 32~200 | 36.0 | 25.0 | ISO 7379 / DIN 9841 |
| 30.0 | M24 | 3.0 | 40~200 | 45.0 | 30.0 | ISO 7379 / DIN 9841 |