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Quick answer
Quick answer: ISO 898-1 property classes
Under ISO 898-1:2013, the class number identifies the minimum tensile-strength family, while the complete table also distinguishes yield or proof-stress values and hardness. For structural or engineered joints, confirm diameter limits, product standard and the required test documents before selecting a class.
| Class | Tensile Rm min (MPa) | Yield / Rp0.2 min (MPa) | Proof stress nominal (MPa) | HV range | Inquiry |
|---|---|---|---|---|---|
| 4.6 | 400 | 240 ReL | 225 | 120–220 | Quote this size |
| 5.6 | 500 | 300 ReL | 280 | 155–220 | Quote this size |
| 8.8 | 800 / 830 | 640 / 660 Rp0.2 | 580 / 600 | 250–320 / 255–335 | Quote this size |
| 10.9 | 1040 | 940 Rp0.2 | 830 | 320–380 | Quote this size |
| 12.9 | 1220 | 1100 Rp0.2 | 970 | 385–435 | Quote this size |
Sourcing these sizes? Property class 10.9 hex bolts ASTM F3125 structural bolts
ISO 898-1:2013 mechanical properties
Values below are the ISO 898-1:2013 Table 3 property-class values for bolts, screws and studs. 8.8 has separate values for d ≤ 16 mm and d > 16 mm in parts of the table; the slash keeps those standard qualifiers visible instead of silently selecting one.
| Property class | Tensile strength Rm min (MPa) | Yield strength min (MPa) | Proof stress nominal Sp (MPa) | Vickers hardness HV | Inquiry |
|---|---|---|---|---|---|
| 4.6 | 400 | 240 ReL | 225 | 120–220 | Quote this size |
| 5.6 | 500 | 300 ReL | 280 | 155–220 | Quote this size |
| 8.8 | 800 / 830 | 640 / 660 Rp0.2 | 580 / 600 | 250–320 / 255–335 | Quote this size |
| 10.9 | 1040 | 940 Rp0.2 | 830 | 320–380 | Quote this size |
| 12.9 | 1220 | 1100 Rp0.2 | 970 | 385–435 | Quote this size |
Bolt head marking under ISO 898-1:2013
For hexagon and hexalobular head bolts with nominal diameter d ≥ 5 mm, the head is marked with the manufacturer identification mark and the property-class symbol. The class symbols are 4.6, 5.6, 8.8, 10.9 and 12.9; the dot may be omitted, and a clock-face system can apply to small screws or heads that cannot take the normal marking.
| Marking item | What to check | Inquiry |
|---|---|---|
| Property-class symbol | 4.6, 5.6, 8.8, 10.9 or 12.9 | Quote this size |
| Manufacturer mark | Required with the class symbol for full-loadability fasteners | Quote this size |
| Diameter threshold | Head marking is required for d ≥ 5 mm unless the product standard provides the applicable exception | Quote this size |
Use the class chart with the product standard
This page is a property-class lookup, not an application design calculation. For the focused comparison of 8.8, 10.9 and 12.9, see the existing 8.8 vs 10.9 vs 12.9 article; it covers selection context separately.
- Call out ISO 898-1:2013 plus the bolt product standard and nominal diameter.
- Request the required mill, mechanical-test and inspection records for the actual lot.
- Do not infer class from surface colour, finish or a catalogue photograph.
Order these sizes from HEXVARO
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Frequently asked questions
What is the tensile strength of an 8.8 bolt?
ISO 898-1:2013 lists a minimum tensile strength Rm of 800 MPa for property class 8.8 bolts with d ≤ 16 mm and 830 MPa for d > 16 mm.
What is the difference between 10.9 and 12.9 bolt classes?
The table lists 10.9 at 1040 MPa minimum tensile strength and 940 MPa minimum Rp0.2 yield strength, while 12.9 is 1220 MPa and 1100 MPa respectively. Product standard and application review still control selection.
What does 4.6 mean on a bolt head?
It is the ISO 898-1 property-class symbol. In this table, class 4.6 has 400 MPa minimum tensile strength, 240 MPa lower yield strength and 225 MPa nominal proof stress.
Where is the property class marked on a hex bolt?
ISO 898-1:2013 says hexagon head bolts are marked preferably on the top of the head, or on the side by indenting; the manufacturer identification mark appears with the property-class symbol.
Products to this standard