Class 12.9 Socket Head Cap Screws
The strongest standard metric class: alloy steel at 1220 MPa (177 ksi) tensile and 1100 MPa yield, 38 to 44 HRC — the socket head cap screw class, equivalent to A574 in inches.
The workhorse of machine parts, die fixturing, and clamping. Standard socket head cap screws in alloy and stainless, imperial and metric, to ASME B18.3.
Class 12.9 is the top of the ISO 898-1 range: 1220 MPa tensile, 1100 MPa yield and a 970 MPa proof load at 38 to 44 HRC, from alloy steel only, tempered at 380 °C minimum. It is the class of the metric socket head cap screw and corresponds to ASTM A574. The specification itself cautions that 12.9 needs tight control of heat treatment, decarburization and surface condition, and that some environments can cause stress-corrosion cracking of plated or unplated product.
Hot-shot or plant down? Call 832-446-3442, answered 24/7.
What Class 12.9 must meet.
| Property class and size | Proof load (MPa) | Tensile strength, min (MPa) | Yield strength, min (MPa) | Elongation, min (%) | Hardness |
|---|---|---|---|---|---|
| 12.9 — M1.6 to M100 | 970 | 1220 | 1100 | 8 | C38–C44 |
Values per ASTM F568M Table 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Proof load and tensile loads by thread size are in Table 5 of the specification.
Quenched in oil from above the transformation temperature and tempered at 380 °C (715 °F) minimum, with fine-grain alloy steel that reaches about 90 percent martensite at the centre. Decarburization and carburization of the thread surface are controlled. Plated parts are baked.
Full Class 12.9 data sheet: chemistry, physical properties and standards →
Made to standard or to your drawing.
- Socket head cap screws for tooling, dies and machinery
- Engine, gearbox and driveline bolting
- Hydraulic manifolds and high-pressure connections
- Racing and high-performance hardware