Technical Guide
Bolt Grade 8.8 vs 10.9
8.8 and 10.9 are property classes under ISO 898-1, the standard that governs mechanical properties of steel fasteners. The two digits aren't arbitrary — they encode the bolt's strength.
How the property class number works
Under ISO 898-1, the first number is 1/100th of the bolt's minimum tensile strength in MPa. The second number, divided by 10, gives the ratio of yield strength to tensile strength.
So grade 8.8 means a minimum tensile strength of roughly 800 MPa, with yield strength at about 80% of that (≈640 MPa). Grade 10.9 means roughly 1000 MPa minimum tensile strength, with yield at about 90% of that (≈900 MPa).
8.8 vs 10.9 at a glance
| Property Class | Min. Tensile Strength | Min. Yield Strength | Typical Use |
|---|---|---|---|
| 8.8 | ≈800 MPa | ≈640 MPa | General structural & mechanical bolting |
| 10.9 | ≈1000 MPa | ≈900 MPa | Higher-load structural & critical mechanical joints |
A note on grade 12.9
ISO 898-1 also defines a 12.9 property class (≈1200 MPa minimum tensile strength) — it's a recognised class in the standard, used for high-load applications such as some automotive and precision machinery fastening. It is not currently part of Kesharia's stocked range; the verified stock runs 4.6 through 10.9 plus HSFG structural bolts (see the table above and the High Tensile Fasteners category below).
Kesharia's verified grade range
- Grade 4.6 / 4.8 — DIN 931, DIN 933, DIN 601, DIN 558
- Grade 5.6 / 5.8 — DIN 960, DIN 961
- Grade 6.8 / 8.8 — ISO 4014–4017, BS 4190, BS 3692, AS 1111, JIS 1180, ASME B18.2.3.1M
- Grade 10.9 — ISO 4016, ISO 4017, SAE J429 Grade 8 equivalent, ASTM A449
- HSFG (High Strength Friction Grip) structural bolts — DIN 6914/6915/6916, ASTM A325/A490, BS 4395
Frequently Asked Questions
Does Kesharia supply grade 12.9 bolts?
Grade 12.9 is not currently part of Kesharia's stocked range. The verified stock covers grades 4.6 through 10.9, plus HSFG structural bolts and ASTM/SAE equivalents — contact us to check availability for a specific requirement.
Can I substitute 10.9 for 8.8 in an existing design?
Not without engineering sign-off. A higher property class changes the bolt's strength and hardness, which affects torque specification, mating nut grade, and the joint's overall behaviour — always confirm with the design engineer before substituting grades.
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