Property Class 12.9 Metric Bolts (ISO 898-1 / ASTM F568M)
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.
What Class 12.9 is.
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.
We machine 12.9 socket head cap screws, bolts and studs in M1.6 to M100 from certified alloy bar, have them heat treated to the specification, and supply them black oxide, zinc-flake coated, or plated with a hydrogen relief bake.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.31 | 0.65 |
| Phosphorus | P | — | 0.045 |
| Sulfur | S | — | 0.045 |
| Alloying elements | — | required | — |
Values per ASTM F568M Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| 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.
Specifications that apply.
How Class 12.9 ships from Houston.
- Hex and heavy hex bolts and cap screws
- Studs and threaded rod
- Nuts and washers to match
- Machined specials to drawing
Class 12.9 fasteners we make.
Every item is manufactured to your drawing or standard in Class 12.9, imperial or metric, with an EN 10204 3.1 certificate.
What is a Class 12.9 bolt?
12.9 means 1200 MPa nominal tensile with yield at 90 percent; the specified minimums are 1220 and 1100 MPa. This is as strong as a standard bolt gets, and the specification says so plainly: capability of the manufacturer and the service environment must be considered, because at 38 to 44 HRC the steel is sensitive to hydrogen, to surface defects and to stress corrosion. Used correctly, with controlled heat treatment and the right finish, it is the standard for socket head cap screws where space is tight and clamp load must be high.
Testing, certification and marking
- Tensile, proof load and hardness tested per lot to ASTM F606
- Grade mark 12.9 and manufacturer's identification on the head or one end
- Certificate of conformance or test report with heat number on request; EN 10204 3.1 available
- Coating thickness reported when plated or galvanized
ASTM A574 Alloy Steel Socket Head Cap Screws (170–180 ksi)
The socket head cap screw specification: alloy steel quenched and tempered to 180 ksi in ½ in. and smaller and 170 ksi above, 37 to 44 HRC, black oxide — the standard for tooling, machinery and die work.
ISO 898-1 · ASTM F568M Class 10.9Property Class 10.9 Metric Bolts (ISO 898-1 / ASTM F568M)
The metric Grade 8: alloy steel quenched and tempered to 1040 MPa (150 ksi) tensile and 940 MPa yield, 33 to 39 HRC — equivalent to A354 BD and A490 in the inch system.
ASTM F912 · ASME B18.3ASTM F912 Alloy Steel Socket Set Screws
The socket set screw specification: alloy steel through hardened to 45 to 53 HRC, torque tested rather than tensile tested, with cup, flat, cone, oval and half-dog points — black oxide finished.