Bolt Grade Chart
Bolt grade is the number that tells you how strong the bolt is. Using the wrong grade on a load-bearing joint can fail the whole assembly. This guide explains the common grades and how to read them.
What Is a Bolt Grade?
A bolt grade indicates the tensile and yield strength of the bolt material. There are two marking systems: imperial (Grade 5, Grade 8) and metric (8.8, 10.9). The higher the number, the stronger the bolt.
Bolt Grade Chart
| Grade | System | Min Tensile Strength | Typical Use |
|---|---|---|---|
| Grade 5 | Imperial | 830 MPa | General structural |
| Grade 8 | Imperial | 1040 MPa | Heavy load |
| Class 8.8 | Metric | 800 MPa | Standard high-strength |
| Class 10.9 | Metric | 1000 MPa | High-load engineering |
How to Read the Grades
Metric grades show strength directly: 8.8 means roughly 800 MPa tensile with a 0.8 yield ratio. Imperial grades are named by class. Always select the grade to match the project's load requirement, and never use a bolt whose grade is below specification.
Inspection
Before reuse, check bolts for stretched threads, corrosion and head markings. A bolt that has been over-tightened or previously loaded beyond its limit should be discarded.
FAQ
Which is stronger, Grade 8 or 10.9?
Class 10.9 (1000 MPa) is stronger than Grade 8 (1040 MPa imperial, 800 MPa metric 8.8). Compare the actual tensile value, not just the name.
Does bolt finish affect strength?
Yes — a finish like stainless steel changes corrosion resistance and strength. See our material guide below.
Related Reading
High-Tensile Bolts
SolidLink supplies high-tensile bolts and nuts in Grades 8.8 and 10.9. Browse our fastener range or contact us for a quote.
