How to choose the correct grade of fastener

Why Steel Grade Matters in Fasteners

Fasteners — bolts, nuts, screws, and washers — may be small, but they are essential to the strength and safety of every structure or machine. Their performance depends largely on the grade of steel used.

Choosing the correct fastener grade ensures durability, mechanical strength, and corrosion resistance — key factors in industrial, automotive, and construction applications.

Let’s explore the most common grades of steel used for fasteners, their advantages, and best-use scenarios.

1. Low Carbon Steel Fasteners (Grades 2, 4.6, 4.8)

Description:
Low carbon steel (0.05–0.25% carbon) is commonly used for non-critical, general-purpose fasteners.

Advantages:

• Cost-effective and easy to produce

• Good ductility and machinability

• Can be zinc-plated or galvanized for mild corrosion resistance

Applications:

• Furniture and household fittings

• Light-duty machinery and fixtures

• General maintenance and assembly

Common Grades:

• ASTM A307 Grade A – General-purpose bolts

• ISO 898-1 Grade 4.6 / 4.8 – Standard low-strength fasteners

2. Medium Carbon Steel Fasteners (Grades 5.8, 8.8)

Description:
Medium carbon steel (0.25–0.55% carbon) is heat-treated (quenched and tempered) for greater strength and hardness.

Advantages:

• Higher tensile and yield strength

• Balanced strength and ductility

• Good fatigue and wear resistance

Applications:

• Automotive suspension and chassis parts

• Machinery components

• Building and structural connections

Common Grades:

• ISO 898-1 Grade 8.8 – Widely used high-tensile bolts

• ASTM A325 – Structural bolts for construction

  
  

3. Alloy Steel Fasteners (Grades 10.9, 12.9)

Description:
Alloy steels include chromium, molybdenum, vanadium, or nickel — providing exceptional strength, toughness, and wear resistance.

Advantages:

• Very high tensile and yield strength

• Excellent fatigue and impact resistance

• Performs well under high stress and vibration

Applications:

• Automotive engines, transmissions, and machinery

• Aerospace and defense equipment

• High-torque and high-temperature environments

Common Grades:

• ISO 898-1 Grade 10.9 / 12.9 – Critical high-performance bolts

4. Stainless Steel Fasteners (Grades A2, A4, 304, 316)

Description:
Stainless steels, rich in chromium and nickel, offer excellent corrosion and oxidation resistance, making them ideal for harsh environments.

Advantages:

• Outstanding corrosion resistance

• Non-magnetic options available

• Aesthetic, clean surface finish

• Long-lasting durability in wet or chemical environments

Applications:

• Marine and offshore construction

• Food, medical, and chemical industries

• Outdoor and architectural fittings

Common Grades:

• A2-70 (304 Stainless Steel) – General-purpose corrosion-resistant bolts

• A4-80 (316 Stainless Steel) – Superior resistance to seawater and chemicals

5. High Tensile Structural Steel Fasteners (ASTM A490, EN 14399)

Description:
These high-strength alloy steel fasteners are heat-treated to withstand extreme loads and vibrations, commonly used in structural and heavy-duty projects.

Advantages:

• Superior load-bearing capacity

• Excellent fatigue strength and toughness

• Reliable in dynamic and static load conditions

Applications:

• Bridges, towers, wind turbines

• Steel buildings and industrial structures

• Offshore platforms and heavy engineering

Common Grades:

• ASTM A490 / A325M – Structural steel bolts

• EN 14399-10 – Preloaded structural assemblies

Comparison Table: Steel Fastener Grades

Choosing the Right Steel Fastener Grade

Before selecting a fastener, consider:

• Load requirements: Shear, tensile, or torque loads

• Environment: Exposure to moisture, salt, or chemicals

• Temperature: Hot or cold conditions

• Corrosion resistance: Indoor vs. outdoor use

• Cost-effectiveness: Performance vs. budget

The right selection ensures safety, durability, and long-term reliability.

Conclusion

Every project demands a specific fastener grade — from low-carbon steel for general use to stainless and high-tensile alloy steels for demanding applications.

Understanding these differences helps engineers and buyers make informed decisions, improving performance, safety, and lifespan.

A well-chosen fastener grade isn’t just a small detail — it’s the foundation of a reliable assembly.