Property Class 8.8 Metric Bolts (ISO 898-1 / ASTM F568M)
The metric Grade 5: medium-carbon steel quenched and tempered to 830 MPa (120 ksi) tensile and 660 MPa yield — the general-purpose high-strength metric bolt, equivalent to A449 and A325.
What Class 8.8 is.
Class 8.8 is the most common heat-treated metric bolt. Under ISO 898-1 and ASTM F568M it is medium-carbon steel quenched and tempered to 830 MPa tensile and 660 MPa yield in M20 and above, at 23 to 34 HRC, with a 600 MPa proof load. It corresponds to SAE Grade 5, ASTM A449 and ASTM A325 in the inch system, and Class 8.8.3 is the weathering-steel version.
We machine 8.8 bolts, screws and studs in M20 to M80 under F568M, and to ISO 898-1 in the smaller sizes, from certified bar, have them quenched and tempered to the specification, and supply them plain, zinc plated or hot-dip galvanized with Class 8 nuts.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon (medium carbon) | C | 0.25 | 0.55 |
| Carbon (low-carbon martensite) | C | 0.15 | 0.40 |
| Manganese (low-carbon martensite) | Mn | 0.74 | — |
| Boron (low-carbon martensite) | B | 0.0005 | — |
| Phosphorus | P | — | 0.048 |
| Sulfur | S | — | 0.058 |
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 |
|---|---|---|---|---|---|
| 8.8 — M20 to M80 (F568M scope) | 600 | 830 | 660 | 12 | C23–C34 |
| 8.8.3 weathering — M20 to M36 | 600 | 830 | 660 | 12 | C23–C34 |
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 8.8 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 8.8 fasteners we make.
Every item is manufactured to your drawing or standard in Class 8.8, imperial or metric, with an EN 10204 3.1 certificate.
What is a Class 8.8 bolt?
8.8 means 800 MPa nominal tensile strength with yield at 80 percent of it; the specified minimums are 830 and 660 MPa. The bolt is quenched and tempered medium-carbon steel, so it hardens through in the normal size range and has the toughness to be tightened to yield. It is the metric bolt on most machinery and structural drawings, and in strength it sits exactly where Grade 5, A449 and A325 sit in inches.
Testing, certification and marking
- Tensile, proof load and hardness tested per lot to ASTM F606
- Grade mark 8.8 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
SAE Grade 5 / ASTM A449 Bolts (120 ksi)
The everyday high-strength bolt: quenched and tempered medium-carbon steel at 120 ksi to 1 in., stepping down for larger sizes — Grade 5 in SAE terms, A449 in ASTM terms.
ASTM F3125/F3125M Grade A325 · Type 1 and Type 3ASTM F3125 Grade A325 Structural Bolts (120 ksi)
The structural steel connection bolt: heavy hex head, 120 ksi tensile, ½ to 1½ in., quenched and tempered, with the twist-off F1852 and metric A325M variants in the same specification.
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.