Introduction

Ever picked up a bolt and noticed markings stamped on the head — numbers, letters, or symbols — and wondered what they mean?

Those markings aren’t random. They tell you:

• The strength of the bolt
• The standard it complies with
• Sometimes even the manufacturer

Understanding these markings is critical for choosing the right fastener and avoiding costly mistakes.

? If you’re unsure about strength ratings, read our Bolt Grades Explained: 8.8 vs 10.9 vs 12.9 | Strength Guide AU - KonnectDirect

What Are Bolt Markings?

Bolt markings are stamped onto the head of a bolt to identify its:

• Grade (strength)
• Standard
• Manufacturer

They act as a quick reference guide on-site, helping you verify you’re using the correct fastener.

How do you read bolt markings?

Bolt markings are read by identifying the numbers or symbols stamped on the bolt head. Metric bolts use numbers such as 8.8 or 10.9 to indicate strength, while structural bolts may include standard markings that show compliance with specifications like AS/NZS 1252.

Common Metric Bolt Markings

What the Numbers Mean:

• 8.8 → General high tensile
• 10.9 → Higher strength
• 12.9 → Maximum strength

Bolt Grades Explained: 8.8 vs 10.9 vs 12.9 | Strength Guide AU - KonnectDirect

Structural Bolt Markings

Structural bolts often include:

• Manufacturer marks
• Standard compliance indicators
• Size references

These markings confirm the bolt meets engineering and safety requirements.

Structural Bolts Guide – Standards, Types, Installation & Specifications - KonnectDirect

Manufacturer Markings

Some bolts include logos or symbols identifying the manufacturer.

This helps:

• Traceability
• Quality assurance
• Compliance verification

Why Bolt Markings Matter

Ignoring bolt markings can lead to:

• Using the wrong grade
• Failing compliance checks
• Structural or mechanical failure

? Always verify markings before installation

Common Mistakes

Ignoring Markings Completely

One of the most common site errors.

Assuming All Bolts Are the Same

Different markings = different performance.

Misreading Grades

Bolt Grades Explained: 8.8 vs 10.9 vs 12.9 | Strength Guide AU - KonnectDirect

Frequently Asked Questions

What do numbers on bolts mean?

They indicate the bolt’s strength and grade.

Are all bolts marked?

No, but most high tensile and structural bolts include markings.

Can you identify bolt grade without markings?

Not reliably — markings are the safest way.

What does 8.8 mean on a bolt?

It represents tensile strength and yield ratio.

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