Metric Bolt, Screw and Nut Strength — ISO 898 Property Classes
ISO 898-1 property classes 3.6 to 12.9 — nominal and minimum tensile strength, lower yield and 0.2% proof stress — plus ISO 898-2 nut-to-bolt class pairing and the ISO 3506 stainless groups and grades with their minimum strengths.
Last updated: 2026-11
Specifications
The property class stamped on a metric bolt or screw is its strength certificate in two numbers: the first digit is 1/100 of the nominal tensile strength in kgf/mm 2 tradition, the second is roughly the ratio of yield (or proof) to tensile. This reference collects the strength tables behind that system in one page. The ISO 898 table covers classes 3.6 through 12.9: nominal tensile from 300 (class 3.6) to 1200 (class 12.9), minimum tensile, and — split by hardening route — lower yield strength R eL,min for the ductile classes 3.6-6.8 (e.g. 4.6: 240) versus 0.2% non-proportional elongation stress R p0.2,min for the hardened classes 8.8 up (e.g. 12.9: 1100). Class 8.8 is split by diameter: up to 16 mm it prints 800/640, above 16 mm 830/660 — the same marking, two strength rows. The ISO 898-2 pairing table follows: a class-8 nut mates up to class 8.8 bolts, a class-10 nut up to 10.9, and so on. The ISO 3506 stainless tables close the page: the austenitic (A1-A5), martensitic (C1/C3/C4) and ferritic (F1) groups, and the grade/class grid with minimum tensile and 0.2% proof stress — A2-70: 700/450, A4-80: 800/600, C1-110: 1100/820. Use it to decode markings, check a pairing, or compare a carbon-steel class against a stainless grade at quotation. Proof loads, test mandates and marking rules are per RFQ against the standards themselves.
| Carbon/n alloy steel classes | 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8 (d <= 16 and d > 16), 9.8, 10.9, 12.9 — nominal tensile 300-1200, min tensile 330-1220 |
|---|---|
| Yield vs proof columns | Classes 3.6-6.8: lower yield R eL,min (180-480); 8.8 and above: 0.2% proof R p0.2,min (640-1100); en-dash cells mark not-tabulated values as printed |
| Nut pairing | Nut class 5 -> bolts up to 5.8; 6 -> 6.8; 8 -> 8.8; 10 -> 10.9; 12 -> 12.9 (where permitted by ISO 898-2) |
| Stainless groups | Austenitic A1/A2/A3/A4/A5, martensitic C1/C3/C4, ferritic F1 per ISO 3506 |
| Stainless grade strengths | Austenitic 50/70/80/100: 500/700/800/1000 min tensile with 210/450/600/750 proof; C1 up to 110 (1100/820); C3-80 (800/640); F1-45 and -60 (450/250, 600/410) |
| Not tabulated | Hardness ranges, proof loads in kN, test frequencies, marking layout, temperature limits — per RFQ |
| Property Class | Nominal Tensile Strength R m,nom | Minimum Tensile Strength R m,min | Lower Yield Strength R eL,min | 0.2% Non-Proportional Elongation Stress R p0.2,min |
|---|---|---|---|---|
| 3.6 | 300 | 330 | 180 | – |
| 4.6 | 400 | 400 | 240 | – |
| 4.8 | 400 | 420 | 320 | – |
| 5.6 | 500 | 500 | 300 | – |
| 5.8 | 500 | 520 | 400 | – |
| 6.8 | 600 | 600 | 480 | – |
| 8.8 – d ≤ 16 mm | 800 | 800 | – | 640 |
| 8.8 – d > 16 mm | 800 | 830 | – | 660 |
| 9.8 | 900 | 900 | – | 720 |
| 10.9 | 1000 | 1040 | – | 940 |
| 12.9 | 1200 | 1220 | – | 1100 |
- Row 1 (3.6): classes 3.6-6.8 carry lower yield strength R eL,min; 8.8 and above carry 0.2% proof R p0.2,min (hardened classes have no distinct yield plateau) — the en-dash cells are the source's own not-tabulated markers
- Row 7 (8.8 – d ≤ 16 mm): class 8.8 is split by diameter (d <= 16 mm vs d > 16 mm) with different R m,min and R p0.2,min — as printed
| Nut Property Class | Typical Mating Bolt Property Class |
|---|---|
| 5 | Up to property class 5.8 where permitted by ISO 898-2 |
| 6 | Up to property class 6.8 where permitted by ISO 898-2 |
| 8 | Up to property class 8.8 where permitted by ISO 898-2 |
| 10 | Up to property class 10.9 where permitted by ISO 898-2 |
| 12 | Up to property class 12.9 where permitted by ISO 898-2 |
| Group | Designation | General Description |
|---|---|---|
| Austenitic | A1, A2, A3, A4, A5 | Chromium-nickel and chromium-nickel-molybdenum stainless steels widely used where corrosion resistance is required. Austenitic grades are generally non-magnetic in the solution-annealed condition but can become partly magnetic after cold working. |
| Martensitic | C1, C3, C4 | Hardenable stainless steels capable of relatively high mechanical strength. Their corrosion resistance is generally lower than that of common austenitic stainless steels. |
| Ferritic | F1 | Chromium stainless steels with magnetic behaviour and mechanical and corrosion properties differing from the austenitic grades. |
| Stainless Group | Grade / Type | Property Class | Minimum Tensile Strength R m (N/mm 2 ) | Minimum 0.2% Proof Stress R p0.2 (N/mm 2 ) |
|---|---|---|---|---|
| Austenitic | A1, A2, A3, A4, A5 | 50 | 500 | 210 |
| 70 | 700 | 450 | ||
| 80 | 800 | 600 | ||
| 100 | 1000 | 750 | ||
| Martensitic | C1 / C4 | 50 | 500 | 250 |
| C1 / C4 | 70 | 700 | 410 | |
| C1 | 110 | 1100 | 820 | |
| Martensitic | C3 | 80 | 800 | 640 |
| Ferritic | F1 | 45 | 450 | 250 |
| 60 | 600 | 410 |
Materials
- The tenant supplies fasteners across these classes — carbon and alloy steel property classes, and stainless to the A2/A4 austenitic grades that dominate industrial demand (the A1-A5/C/F designations on this page map to those supply grades). State the property class or stainless grade, the size, and any certificate requirement (EN 10204 3.1) on the RFQ; strength values are delivered against the standard and the certificate, and class pairings (bolt + nut) are honoured as specified
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (Metric Bolt, Screw and Nut Strength — ISO 898 Property Classes) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
How do I read a property-class marking like 8.8 or 10.9 into actual strength numbers?
Use the two digits as a shorthand and this page's table as the exact values. For 8.8: the 8 signals a nominal tensile strength of 800 (units as tabulated) and the .8 that yield/proof is 0.8 times that — check the table row and you find proof 640 for sizes up to 16 mm. For 10.9: nominal 1000, proof at 0.9 of it = 900... the table prints 940, because the standard rounds the relationship per class rather than deriving it — this is exactly why you read the table instead of computing. One trap the table makes visible: class 8.8 has two rows (d <= 16 mm: 800/640; d > 16 mm: 830/660), so a big M 24 "8.8" bolt is actually held to a higher minimum than an M 10 one. And the yield/proof column switches meaning at 8.8 — ductile classes report lower yield, hardened classes report 0.2% proof, because hardened steel has no flat yield plateau.
Does a class-10 nut on a class-8.8 bolt work, and what does the stainless A2-70 marking mean?
Yes — and it is deliberate. The pairing table says a class-10 nut mates bolts up to class 10.9, so class-10 on an 8.8 bolt is a valid, slightly over-strong nut choice; the reverse (an 8 nut on a 10.9 bolt) is not, because the nut threads would strip before the bolt reached its strength. Over-specifying the nut is the cheap insurance most joint designers accept. For stainless: A2-70 decodes as austenitic grade (A2 is the common 304-family), property class 70 — the 70 is 1/10 of the minimum tensile strength, 700, with 0.2% proof 450 from this page's table. The same grade can come as A2-50 (soft, 500/210) or A2-80 (800/600, cold-worked), which is why "A2" alone is not a strength statement — always quote grade plus class (A2-70, A4-80) on the RFQ so the certificate matches the marking.
Related knowledge
- Thread-Forming vs Thread-Cutting vs Thread-Rolling Self-Tapping Screws: What the Evidence Settles on Base Material
- Screw Family Selection by Base Material: Wood, Machine and Self-Tapping Threads, Engagement and Coating
- Hex Bolts vs Socket Head Cap Screws: What the Evidence Settles on Strength, Clearance and Cost
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support