alloy-steelISO 898-1
Property Class 12.9
Highest standard property class. Very high preload; hydrogen embrittlement risk when electroplated.
Tensile Rm1220 MPa
Yield Rp0.21100 MPa
HardnessHRC 39–44
Nut class12
Mechanical properties
- Property class
- Property Class 12.9
- Defined in
- ISO 898-1
- Tensile strength Rm (min)
- 1220 MPa
- Yield strength Rp0.2 (min)
- 1100 MPa
- Hardness
- HRC 39–44
- Matching nut class
- 12
- Material
- Alloy Steel
Where this grade is used
The property class is stamped on the head of bolts and screws of M5 and larger, so a 12.9 bolt is marked 12.9. A Property Class 12.9 fastener is specified where the joint needs a 0.2 % proof strength of about 1100 MPa or less. Always pair it with a nut of ISO 898-2 class 12 or higher, so the bolt fails before the thread strips.