Understanding Fastener Grades
A Complete Guide to Strength, Durability, and Performance
When selecting fasteners for any application—whether it’s for automotive, structural, industrial, or marine use—understanding material grades is essential. Fastener grades indicate a bolt or screw’s strength, hardness, and performance under tension and stress. Choosing the right grade ensures safety, longevity, and reliability of your project.
SAE Fastener Grades (Imperial)
Grade 2
Low Stress Applications
Material: Low or medium carbon steel
Tensile Strength: 60,000 – 74,000 psi
Markings: No lines on bolt head
Use Case: Light-duty hardware, home projects, non-critical automotive repairs
Grade 5
Medium Strength
Material: Medium carbon steel, heat-treated
Tensile Strength: 105,000 – 120,000 psi
Markings: Three radial lines on bolt head
Use Case: Automotive components, machinery, equipment requiring more strength than Grade 2
Grade 8
High Strength
Material: Medium carbon alloy steel, quenched and tempered
Tensile Strength: ~150,000 psi
Markings: Six radial lines on bolt head
Use Case: High-stress applications, suspension systems, heavy machinery, structural connections
Grade 9
Maximum Strength
Material: Alloy steel, heat-treated
Tensile Strength: ~180,000 psi
Markings: Often nine radial lines (not standardized)
Use Case: High-torque and maximum-load environments, military-grade or aerospace uses
Metric Fastener Grades
Grade 4.6
Tensile Strength: ~60,000 psi (400 MPa)
Yield Strength: ~36,000 psi (240 MPa)
Use: Basic general-purpose metric fastener; low strength applications
Grade 8.8
Tensile Strength: ~120,000 psi (800 MPa)
Yield Strength: ~85,000 psi (640 MPa)
Use: Automotive and structural applications
Grade 10.9
Tensile Strength: ~150,000 psi (1,040 MPa)
Yield Strength: ~130,000 psi (940 MPa)
Use: Suspension systems, structural bolting, engine components
Grade 12.9
Tensile Strength: ~175,000 psi (1,220 MPa)
Yield Strength: ~160,000 psi (1,100 MPa)
Use: Strongest standard metric fasteners; high-torque precision engineering
Stainless Steel Fastener Grades
Important Note:
Stainless fasteners are primarily chosen for their corrosion resistance, not necessarily their strength.
18-8 Stainless (A2)
Composition: 18% chromium, 8% nickel
Strength: Comparable to Grade 2
General-purpose corrosion-resistant applications
304 Stainless
Very similar to 18-8 with slightly different alloy balance
Food industry, marine settings, general outdoor applications
316 Stainless (A4)
Special Feature: Includes molybdenum for superior corrosion resistance
Marine, saltwater, and chemical exposure environments
410 Stainless
Hardness: Can be heat treated for strength
Corrosion: Lower than 304 or 316
More strength than other stainless; best for dry environments
17-4 PH Stainless
Special Feature: Precipitation hardened for strength
Aerospace, defense, and high-performance equipment
Why Fastener Grade Matters
Structural Integrity
Ensures your project can handle the intended load
️
Safety Under Load
Prevents catastrophic failure under stress
⏰
Long-term Durability
Reduces maintenance and replacement costs
✅
Code Compliance
Meets engineering specifications and regulations
⚠️ Critical Warning
Underrating fastener grade can result in product failure, safety hazards, or expensive downtime. Always consult with engineering specifications and consider safety factors when selecting fasteners for critical applications.
Related Topics:
#FastenerGrades
#Grade2Bolts
#Grade5vsGrade8
#MetricBoltStrength
#StainlessSteelBolts
#HighStrengthFasteners
#BoltMaterialGuide
#IndustrialBolts