ISO 898-1: Bolt Grades 8.8, 10.9 Explained
Verified by Mel Sykes, Industrial Supply Chain Specialist - April 2026
Understanding ISO 898-1
ISO 898-1 specifies the mechanical properties of fasteners made from carbon steels and carbon alloy steels. ISO 898-1 - Mechanical Properties of Fasteners It sets out requirements for tensile strength, yield strength, and hardness for bolts, screws, and studs up to a nominal diameter of 36 mm.
ISO 898-1 is critical because it ensures consistency in fastener quality across different manufacturers. This standard applies to various products including bolts, screws, nuts, and studs made from carbon steels or alloyed carbon steels. It doesn't cover stainless steel fasteners, which are addressed by ISO 3506-1.
The standard defines mechanical properties like tensile strength, yield strength, and elongation at break for different diameter ranges. For instance, a bolt with a nominal diameter of 24 mm must meet specific requirements: its minimum tensile strength is 8.8 MPa, while the yield point ratio (Rp0.2) should be at least 65% of the specified tensile strength.
Which Products Does ISO 898-1 Apply To?
ISO 898-1 applies to a range of fasteners including bolts, screws, studs, and nuts made from carbon steels or alloyed carbon steels. It doesn't cover stainless steel products, which are governed by ISO 3506-1.
The standard covers fastener types such as hexagon head bolts (ISO 4017). Self-tapping screws (ISO 7380), and machine nuts (ISO 4162). For example, a hexagon head bolt manufactured to meet the requirements of ISO 898-1 must have a specified tensile strength range based on its nominal diameter. A bolt with a nominal diameter of 16 mm would need to have a minimum tensile strength of 800 MPa.
Key Technical Requirements in ISO 898-1
ISO 898-1 outlines critical mechanical properties for fasteners, such as tensile strength, yield strength, and elongation at break. These properties are defined based on the nominal diameter of the fastener, with specific values given for each grade.
For instance, a bolt graded 8.8 will have a minimum tensile strength of 800 MPa and a yield point ratio (Rp0.2) of at least 65% of the specified tensile strength. Additionally, ISO 898-1 includes requirements for hardness testing, ensuring that fasteners meet stringent quality standards.
The standard also specifies dimensional tolerances and surface finish requirements to ensure interchangeability across different manufacturers and applications. At ISO 898-1 - Mechanical Properties of Fasteners, for example, a grade 8.8 bolt must comply with specific length and thread pitch tolerances outlined in ISO 2745.
How Engineers Use ISO 898-1
Engineers use ISO 898-1 to specify fastener requirements for design and procurement. They select appropriate grades based on the mechanical load and environmental conditions, ensuring durability and safety.
For example, when designing a structural joint that will experience high tensile loads, an engineer might choose grade 10.9 bolts due to their higher strength (minimum tensile strength of 1040 MPa). Engineers also refer to ISO 898-1 during quality control inspections to verify that fasteners meet specified mechanical properties.
Relationship with Other Standards
ISO 898-1 complements other standards such as DIN EN ISO 3506 for stainless steel fasteners and BS EN ISO 2745 for bolt dimensions. It's also aligned with the British Industrial Fasteners Association (BIAFD) guidelines, ensuring a cohesive approach to fastener specification.
For instance, when designing assemblies that require both carbon steel and stainless steel components, engineers can refer to ISO 898-1 and ISO 3506 side by side. This ensures consistent quality across different materials while adhering to industry best practices set by the British Fasteners Technology Association (BTMA) and the British Precast Concrete Federation (BPMA).
ISO 898-1 is important for ensuring that fasteners meet international standards, facilitating smooth integration into diverse engineering projects worldwide.
References
Frequently Asked Questions
What does ISO 898-1 cover?
ISO 898-1 (ISO 898-1 - Mechanical Properties of Fasteners) specifies requirements for fasteners-fixings. It is issued by ISO and widely used in UK engineering procurement and manufacturing.
Is ISO 898-1 mandatory in the UK?
ISO 898-1 is not law, but it is referenced in most UK engineering specifications and procurement contracts. Many buyers require compliance as a condition of supply.
What materials are covered by ISO 898-1 - Mechanical Properties of Fasteners?
ISO 898-1 covers fasteners made from carbon steels and carbon alloy steels, but it doesn't include stainless steel products which fall under the scope of ISO 3506-1.
What are the mechanical properties defined for bolts with a nominal diameter of 24 mm in ISO 898-1?
For bolts with a nominal diameter of 24 mm as per ISO 898-1, the minimum tensile strength is specified at 830 MPa and the yield point ratio (Rp0.2) should be at least 65% of the specified tensile strength.
Which types of fasteners are included in ISO 898-1 - Mechanical Properties of Fasteners?
ISO 898-1 includes various fastener types such as bolts, screws, studs, and nuts made from carbon steels or alloyed carbon steels, ensuring uniform quality across different manufacturers.
How do UK engineers choose between the variants of ISO 898-1 for their projects?
Engineers should select the appropriate variant based on the mechanical requirements of their project. For instance, choosing between grades like 4.6 and 8.8 involves considering factors such as tensile strength and yield strength required for the specific application.
What does ISO 898-1: Bolt Grades 8.8, 10.9 Explained specify?
ISO 898-1 specifies the mechanical properties of fasteners made from carbon steels and alloyed carbon steels, including tensile strength requirements like a minimum value of 640 MPa for grade 8.8 bolts.
What are the key differences between bolt grades 8.8 and 10.9 as defined in ISO 898-1?
Grade 8.8 bolts have a yield strength that's at least 64% of their tensile strength, while grade 10.9 bolts must meet a higher requirement with a yield strength of at least 90% of the specified tensile strength.
How do UK engineers determine which bolt grade to use according to ISO 898-1?
Engineers should choose between grades 8.8 and 10.9 based on the mechanical loads and stresses involved in their application, with grade 10.9 offering higher strength properties for more demanding conditions.
Where can UK engineers find suppliers of fasteners conforming to ISO 898-1 standards?
UK engineers can visit mlc.org.uk or other reputable industrial supply chain websites to find suppliers of fasteners that meet the ISO 898-1 standard, ensuring quality and compliance for their projects.