Metric Property Class 12.9
Class 12.9 is the highest common metric property class. You will most often see it on alloy socket head cap screws.
| Marking | 12.9 plus manufacturer ID |
|---|---|
| Matching nut | ISO 898-2 class 12 |
| Typical product | ISO 4762 / DIN 912 socket head cap screw |
Mechanical properties (ISO 898-1)
| Class | Tensile Rm (min) | Yield Rp0.2 (min) | Proof stress | Hardness |
|---|---|---|---|---|
| 12.9 | 1220 MPa | 1100 MPa | 970 MPa | 39 - 44 HRC |
Nominal tensile 1200 MPa; the minimum is 1220 MPa.
These tables carry the same figures as the printed sheet below.
The printed sheet
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Text version of this sheet
ISO 898-1 · property class 12.9 · very high strength
What it is
FIELD IDENTIFICATION
Class 12.9 is the highest common metric property class. You will most often see it on alloy socket head
cap screws.
MFG
12.9
12.9
SOCKET HEAD
HEX HEAD
Marking
12.9 plus manufacturer ID
Matching nut
ISO 898-2 class 12
Typical product
ISO 4762 / DIN 912 socket head cap screw
12.9 is most common on socket head cap
screws
Mechanical properties (ISO 898-1)
Class
12.9
Tensile Rm (min)
Yield Rp0.2 (min)
1220 MPa
Proof stress
1100 MPa
Hardness
970 MPa
39 - 44 HRC
Nominal tensile 1200 MPa; the minimum is 1220 MPa.
Key points
At this hardness, electroplating can cause delayed hydrogen-embrittlement fracture hours or days after tightening. Avoid electroplated 12.9 unless the
process is qualified and baked; zinc-flake coatings are the usual alternative.
Needs a fully engaged, adequately strong internal thread. Soft tapped holes strip before the screw.
Governing standards: ISO 898-1:2013; ISO 898-2:2022; ISO 4762:2004. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard
always take precedence over this sheet.
torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability
arising from reliance on this reference.
Fastener Guide reference FG-CA6D41 · thefastenerapp.com/fastener-guide/technical-reference/metric-property-class-12-9 · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
