Bolt Grades Explained: 8.8 vs 10.9 vs 12.9 | Strength Guide AU
30th Mar 2026
Introduction
If you’ve ever looked at a bolt head and seen numbers like 8.8, 10.9, or 12.9, you’re looking at its grade — and it directly impacts strength, performance, and safety.
Choosing the wrong grade can lead to:
- Equipment failure
- Safety risks
- Costly downtime
In this guide, we break down exactly what bolt grades mean and when to use each.
? If you're comparing applications, read our High Tensile vs Structural Bolts: What’s the Difference (and When to Use Each) - KonnectDirect
What Do Bolt Grades Mean?
Bolt grades indicate:
- Tensile strength (maximum load before breaking)
- Yield strength (point where deformation begins)
Simple Explanation:
- First number = tensile strength (x100 MPa)
- Second number = yield percentage
? Example:
- 8.8 = 800 MPa tensile, 640 MPa yield
What do bolt grades 8.8, 10.9 and 12.9 mean?
Bolt grades indicate the strength of a bolt. The first number represents tensile strength, and the second number represents the yield ratio. For example, grade 8.8 has a tensile strength of 800 MPa and yields at 80% of that strength.
Bolt Grade Comparison
| Grade | Tensile Strength | Yield Strength | Typical Use |
|---|---|---|---|
| 8.8 | 800 MPa | 640 MPa | General applications |
| 10.9 | 1000 MPa | 900 MPa | Heavy-duty |
| 12.9 | 1200 MPa | 1080 MPa | High-performance |
Grade 8.8 Bolts Explained
Grade 8.8 bolts are the most common high tensile bolts used across general applications.
? Buy Bolts Online | Hex, U-Bolts & More - Konnect Direct
Grade 10.9 Bolts Explained
Grade 10.9 bolts provide higher strength and are suited to heavy-duty environments.
Grade 12.9 Bolts Explained
Grade 12.9 bolts are among the strongest available and are used in critical applications.
⚠️ Not typically used for structural steel.
When Should You Use Each?
Use 8.8 When:
- General applications
- Moderate loads
Use 10.9 When:
- Higher loads
- Heavy equipment
Use 12.9 When:
- Maximum strength required
- Space constraints
Common Mistakes
- Assuming higher grade = better
- Ignoring application requirements
- Confusing grade with structural compliance
High Tensile vs Structural Bolts: What’s the Difference (and When to Use Each) - KonnectDirect
Frequently Asked Questions
What is the strongest bolt grade?
Grade 12.9 is one of the strongest standard metric bolt grades.
Is 10.9 stronger than 8.8?
Yes, 10.9 bolts are stronger and used in higher load applications.
Can I use 12.9 bolts for structural steel?
No, structural applications require compliance with standards like AS/NZS 1252.
What bolt grade should I use?
It depends on load, environment, and compliance requirements.