ISO 898-1 — property classes for carbon and alloy steel bolts, screws and studs
What ISO 898-1 actually requires: the property class table, hardness limits, minimum tempering temperature, surface-vs-core hardness and decarburization rules, and what to write on the drawing.
| Related service | Heat Treatment |
|---|---|
| Mechanical properties | ISO 898-1 |
| Also written as | ISO 898-1:2013, EN ISO 898-1, JIS B 1051, SAE J429 (inch counterpart) |
| Updated |
Scope — and what it does not cover
ISO 898-1 sets the mechanical and physical properties of bolts, screws and studs made of carbon steel and alloy steel, tested at room temperature, for coarse and fine pitch threads roughly M1.6 to M39. It defines the property classes (4.6 up to 12.9) and the tensile, proof load, hardness, decarburization and — for the quenched and tempered classes — the minimum tempering temperature. It does NOT cover nuts (ISO 898-2), stainless fasteners (ISO 3506), set screws, coatings and plating (ISO 4042), locking performance, or behaviour at elevated or sub-zero temperature.
Standards are copyrighted documents. We explain scope, intent and practical application in our own words; obtain the current edition from ISO, ASTM, DIN or your national standards body.
What actually bites in production
- 1The class code is arithmetic, not branding: the first number is nominal tensile strength ÷ 100 MPa, the second is ten times the ratio of yield to tensile. A 10.9 bolt is nominally 1 000 MPa with yield at about 90 % of it.
- 2Hardness has a MAXIMUM as well as a minimum. A 10.9 bolt measured at 400 HV is not "extra good" — it is out of class, and it has moved into the hydrogen-embrittlement risk band.
- 3Classes 8.8 and above must be quenched and tempered above the minimum tempering temperature (425 °C in the current edition). Reaching the hardness band by another route does not conform.
- 4Surface hardness must not exceed core hardness by more than 30 Vickers points, both measured at HV 0.3. This is the clause that catches unintended carbon pick-up from the furnace atmosphere.
- 5Decarburization is limited: no complete decarburization deeper than about 0.015 mm, and a minimum unaffected thread height that rises with the class (about ½ H1 for 8.8, ⅔ H1 for 9.8 and 10.9, ¾ H1 for 12.9).
- 6Full-size fastener tests — proof load, wedge tensile — are the referee. Hardness on a prepared section is a fast production check, not the acceptance test.
Reference tables
Scroll the table sideways on a narrow screen.
Property class → strength → hardness
| Property class | Tensile Rm min (MPa) | Proof stress Sp (MPa) | Hardness (HV) | Hardness (HRC) |
|---|---|---|---|---|
| 4.6 | 400 | 225 | 120–220 | — |
| 4.8 | 420 | 310 | 130–220 | — |
| 5.6 | 500 | 280 | 155–220 | — |
| 5.8 | 520 | 380 | 160–220 | — |
| 6.8 | 600 | 440 | 190–250 | — |
| 8.8 (d ≤ 16 mm) | 800 | 580 | 250–320 | 22–32 |
| 8.8 (d > 16 mm) | 830 | 600 | 255–335 | 23–34 |
| 9.8 (d ≤ 16 mm) | 900 | 650 | 290–360 | 28–37 |
| 10.9 | 1040 | 830 | 320–380 | 32–39 |
| 12.9 | 1220 | 970 | 385–435 | 39–44 |
Values from the class tables; the edition in force governs. Hardness has an upper limit as well as a lower one.
Values on this page are typical industry figures that depend on the part, the coating system and the governing specification. They are not guarantees. Always confirm against the edition in force and the customer drawing — this page does not replace either.
What to write on the drawing or PO
- The class written in full — "ISO 898-1 class 10.9", not "grade 10.9" — with the thread designation and pitch.
- Which acceptance tests are required per lot: proof load, wedge tensile, hardness, decarburization, surface-versus-core hardness.
- Whether testing is on the full-size fastener or a machined test piece, and who supplies the sample.
- The coating specification as a separate line (ISO 4042 / ASTM B633 / F1941) and whether de-embrittlement baking is required — ISO 898-1 does not imply it.
- Any customer limit tighter than the class, for example a narrower hardness window for a torque-tension requirement. Otherwise the full class band applies.
What goes wrong when it is cited loosely
- "Minimum 32 HRC" written alone. The class also has an upper limit; without it a heat treater has no aim point and no basis to reject an over-hard lot.
- Citing ISO 898-1 for stainless fasteners. A2-70 and A4-80 are ISO 3506 designations and are not property classes in the 898-1 sense.
- Assuming the matching nut comes with the bolt class. Nut classes are in ISO 898-2, and a class 8 nut is not "class 8.8".
- Taking a hardness reading through the plating and calling it the class check. The coating has to be removed or a section prepared.
Defects this standard gets cited on
Steel grades where this decision is made
Part types we process to this
Frequently asked questions
Is class 10.9 the same as SAE J429 grade 8 or ASTM A574?+
No. They are different specification systems with different property tables and test methods. Grade 8 is close to 10.9 in strength but not interchangeable on paper — if the drawing says one, do not deliver the other without written agreement.
Can a lot that came out too hard be re-tempered?+
Usually yes, if the material and the drawing allow it and the tempering temperature stays above the class minimum. Re-tempering affects the whole lot, so it is recorded, and hardness, proof load and decarburization are re-checked afterwards.
Does ISO 898-1 say anything about zinc plating?+
It does not specify a coating, but it decides one plating question for you: hardness above roughly 320 HV — class 10.9 and up — is the band in which ISO 4042 calls for hydrogen-embrittlement relief after electroplating.
Values on this page are typical industry figures that depend on the part, the coating system and the governing specification. They are not guarantees. Always confirm against the edition in force and the customer drawing — this page does not replace either.
Related standards
Other standards in this reference
Send the drawing and let us check it against this standard
Send the drawing or the specification line as it is written today, the property class or coating requirement, the thread and tolerance class, and the part itself if you have one. We will tell you which lines are processable as written, which are arithmetically impossible on that thread, and what has to be added before the requirement can be quoted, inspected and defended.
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