ISO 898-1:2023
Mechanical properties
Sets out the mechanical requirements, property classes and test methods applicable to carbon steel and alloy steel fasteners.
ISO 898-1:2023 · Metric system
Metric hex bolts
Classes 5.8, 8.8, 10.9 and 12.9
A technical guide for comparing strength, heat treatment and applications according to the class marked on the bolt head.
ISO 898-1
High metric strength
Up to 1200 MPa
Applicable standards
Three essential references.
ISO 4014:2022
Partial thread
Current dimensional standard for hex head bolts with partial thread; it supersedes the DIN 931 reference.
ISO 4017:2022
Full thread
Current dimensional standard for hex head bolts with full thread; it supersedes the DIN 933 reference.
Quick identification
The class sets the strength and the yield ratio.
The first number indicates the nominal tensile strength; the second defines the ratio between yield strength and tensile strength.
5.8 + manufacturer mark
Class 5.8
500 MPa
Minimum tensile
- Yield strength
- 400 MPa · Ratio 0.8
- Application
- Light machinery, structures and general use
8.8 + manufacturer mark
Class 8.8
800 MPa
Minimum tensile
- Yield strength
- 640 MPa · Ratio 0.8
- Application
- Construction, machinery and industrial equipment
10.9 + manufacturer mark
Class 10.9
1000 MPa
Minimum tensile
- Yield strength
- 900 MPa · Ratio 0.9
- Application
- Mining, power, heavy machinery and automotive
12.9 + manufacturer mark
Class 12.9
1200 MPa
Minimum tensile
- Yield strength
- 1080 MPa · Ratio 0.9
- Application
- Critical high-strength applications, moulds and precision equipment
Comparison sheet
ISO 898-1 technical specifications
Comparison adapted to every screen size.
Class 5.8
- Material
- Carbon steel
- Heat treatment
- Normalised or rolled
- Minimum tensile strength
- 500 MPa
- Minimum yield strength
- 400 MPa
- Yield to tensile ratio
- 0.8
- Typical hardness
- ≈ HB 155–250
- Head marking
- 5.8 + manufacturer mark
- Typical applications
- Light machinery, structures and general use
- Coatings per the standard
- Black, zinc plated, galvanized
- Approximate SAE equivalent
- Grade 2
Class 8.8
- Material
- Medium carbon steel
- Heat treatment
- Quenched and tempered
- Minimum tensile strength
- 800 MPa
- Minimum yield strength
- 640 MPa
- Yield to tensile ratio
- 0.8
- Typical hardness
- ≈ HRC 22–32
- Head marking
- 8.8 + manufacturer mark
- Typical applications
- Construction, machinery and industrial equipment
- Coatings per the standard
- Black, zinc plated, galvanized*
- Approximate SAE equivalent
- Grade 5
Class 10.9
- Material
- Alloy steel
- Heat treatment
- Quenched and tempered
- Minimum tensile strength
- 1000 MPa
- Minimum yield strength
- 900 MPa
- Yield to tensile ratio
- 0.9
- Typical hardness
- ≈ HRC 32–39
- Head marking
- 10.9 + manufacturer mark
- Typical applications
- Mining, power, heavy machinery and automotive
- Coatings per the standard
- Black, zinc flake, fluoropolymers**
- Approximate SAE equivalent
- Grade 8
Class 12.9
- Material
- Alloy steel
- Heat treatment
- Quenched and tempered
- Minimum tensile strength
- 1200 MPa
- Minimum yield strength
- 1080 MPa
- Yield to tensile ratio
- 0.9
- Typical hardness
- ≈ HRC 39–44
- Head marking
- 12.9 + manufacturer mark
- Typical applications
- Critical high-strength applications, moulds and precision equipment
- Coatings per the standard
- Black, zinc flake, fluoropolymers**
- Approximate SAE equivalent
- Above Grade 8
Technical notes
Considerations for selecting the coating and preserving the performance of the bolt.
- 1Hot-dip galvanizing for Class 8.8 requires allowing for tolerances and thread overtapping.
- 2For classes 10.9 and 12.9, electroplated coatings and hot-dip galvanizing are not recommended because of the risk of hydrogen embrittlement. To reduce that risk, apply ASTM F3393-24.
Technical support
Need to confirm the right metric class for your application?
Send us the size, thread pitch, quantity, class and finish on WhatsApp. Our technical team will help you review the requirement.