Property Classes 4.6 and 5.8 Metric Bolts (ISO 898-1 / ASTM F568M)
The metric low-strength classes: 4.6 at 400 MPa (58 ksi), the metric A307, and 5.8 at 520 MPa (75 ksi) cold worked — for general bolting, threaded rod and anchors.
What Class 4.6 / 5.8 is.
Metric property classes name the bolt by its strength: the first number is tensile strength in hundreds of MPa and the decimal is the yield-to-tensile ratio. Class 4.6 is 400 MPa tensile with a 240 MPa yield point, not heat treated, and corresponds to ASTM A307. Class 5.8 is 520 MPa from cold-worked medium-carbon steel. Both are covered by ISO 898-1 and by ASTM F568M, its inch-system counterpart.
We machine 4.6 bolts, studs and threaded rod in M5 to M100, and 5.8 in M5 to M24, from certified bar and supply them plain, zinc plated or hot-dip galvanized with Class 5 or 8 nuts.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon, 4.6 | C | — | 0.55 |
| Carbon, 5.8 | C | 0.13 | 0.55 |
| 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 |
|---|---|---|---|---|---|
| 4.6 — M5 to M100 | 225 | 400 | 240 (yield point) | 22 | B67–B95 |
| 5.8 — M5 to M24 | 380 | 520 | 420 | 10 | B82–B95 |
Values per ASTM F568M Table 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How Class 4.6 / 5.8 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 4.6 / 5.8 fasteners we make.
Every item is manufactured to your drawing or standard in Class 4.6 / 5.8, imperial or metric, with an EN 10204 3.1 certificate.
Reading a property class
A metric bolt marked 4.6 has a nominal tensile strength of 4 × 100 = 400 MPa and a yield of 0.6 × 400 = 240 MPa. Class 5.8 is 500 MPa nominal, 520 specified, with yield at 0.8 of tensile. The system runs all the way to 12.9, and the same logic tells you the strength of any class at a glance, which is the reason it replaced the older letter grades.
Testing, certification and marking
- Tensile, proof load and hardness tested per lot to ASTM F606
- Grade mark 4.6 or 5.8 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
ASTM A307 Grade A and B Bolts (60 ksi)
The general-purpose carbon steel bolt: 60 ksi tensile, not heat treated, weldable and galvanizable — Grade A for general use, Grade B for flanged pipe joints with a 100 ksi cap.
ISO 898-1 · ASTM F568M Class 8.8Property 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.
ASTM A108 cold-finished bar · chemistry per ASTM A29 / SAE J4031018 Carbon Steel (UNS G10180)
The everyday machining steel: low carbon, easily welded and case hardened, cold drawn for a clean finish — for pins, spacers, brackets and non-critical machined parts.