How to Choose the Right Bolt Grade (4.6, 8.8, 10.9, 12.9)
Learn the differences between bolt grades 4.6, 8.8, 10.9, and 12.9. Understand strength, applications, and how to choose the right grade for your project.
How to Choose the Right Bolt Grade for Your Project (4.6, 8.8, 10.9, 12.9)
By Bait Alnuhas | Trusted Fasteners Partner Across the UAE and Beyond
When it comes to structural integrity, the grade of the bolt you choose can make or break your project. Bolts are the backbone of every assembly—whether it's holding together steel beams, heavy machinery, or critical infrastructure.
But not all bolts are created equal. They're classified into grades (like 4.6, 8.8, 10.9, and 12.9) that indicate their strength and performance characteristics. In this article, we'll break down what these grades mean and how to select the right one for your application.
What Do Bolt Grades Mean?
Bolt grades (or property classes) are defined according to ISO 898-1 standards. The numbers tell you two important things:
First number (before the dot): 1/100 of the nominal tensile strength in MPa
Second number (after the dot): Ratio of yield strength to tensile strength
Example: Grade 8.8 means:
Tensile strength = 800 MPa
Yield strength = 0.8 × 800 = 640 MPa
Common Bolt Grades and Their Properties
GradeMaterial TypeTensile Strength (MPa)Yield Strength (MPa)Typical Use Cases4.6Low carbon steel400240Light duty, general purpose, low-stress joints8.8Medium carbon steel, quenched & tempered800640Structural steel, automotive parts, machinery10.9Alloy steel, quenched & tempered1000900Heavy machinery, automotive suspensions, industrial joints12.9Alloy steel, quenched & tempered12001080High-load, critical components, aerospace, precision tooling
Key takeaway: Higher grade = stronger bolt (but also less ductile and more expensive).
How to Choose the Right Grade
Ask yourself these four critical questions before selecting a bolt grade:
1. What Load Will It Carry?
Light loads → Grade 4.6
Medium to heavy loads → Grade 8.8
Very high loads or shock loads → Grade 10.9 or 12.9
2. What Environment Will It Operate In?
Indoor, dry → All grades are acceptable
Outdoor / humid → Prefer stainless steel (A2, A4) or coated high-strength bolts
Corrosive / marine → Combine high tensile + corrosion-resistant coatings
3. What Are the Safety and Compliance Requirements?
Structural projects often mandate 8.8 or higher
Heavy equipment and industrial machines typically require 10.9 or 12.9
Always refer to engineering specifications and local building codes
4. How Important is Cost vs Durability?
4.6 and 8.8 are cost-effective and widely available
10.9 and 12.9 are premium grades — higher cost but long-term reliability
Expert Tip from Bait Alnuhas
Always pair correct grade bolts with matching nuts and washers of the same grade or higher. Mixing low-grade nuts with high-grade bolts can cause premature joint failure.
Why Bait Alnuhas is the Go-To Supplier for High-Grade Bolts
As a trusted fasteners supplier in the UAE, Bait Alnuhas offers:
Full Range
ISO-certified bolt grades (4.6, 5.6, 8.8, 10.9, 12.9)
Bulk Availability
For construction, oil & gas, marine, and manufacturing sectors
Technical Guidance
Expert advice to choose the correct grade for your application
Export Ready
Export-ready packaging and compliance documents
We help you build with confidence, safety, and strength.
Bottom Line
Choosing the right bolt grade ensures your structure stays safe, durable, and compliant.
Grade 4.6
Light duty applications - General purpose, low-stress joints where cost is a primary consideration.
Grade 8.8
Standard structural strength - The most common grade for construction, automotive, and machinery applications.
Grade 10.9 / 12.9
High-strength for critical joints - For heavy machinery, high-load applications, and critical structural components.
Need Expert Help Selecting the Right Bolt Grade?
Contact Bait Alnuhas today to get engineer-approved high-grade bolts tailored to your project requirements.