Fastener Material Guide
Fastener Material & Coating Guide
Selecting the right material and finish is critical for fastener performance. This guide covers common materials, their properties, corrosion resistance ratings, and recommended applications.
Carbon & Alloy Steel
| Material | Tensile Strength | Corrosion Resistance | Temperature Range | Typical Grades | Best For |
|---|---|---|---|---|---|
| Low Carbon (1006–1022) | Low–Medium | Poor (requires plating) | -40°F to 500°F | Grade 2, A307 | General fastening, non-structural |
| Medium Carbon (1035–1045) | High | Poor (requires plating) | -40°F to 600°F | Grade 5, A325 | Automotive, machinery, structural |
| Alloy Steel (4037–8740) | Very High | Poor (requires plating) | -40°F to 800°F | Grade 8, A490, A354 BD | Heavy equipment, high-stress |
Metric Bolt Classes (ISO 898-1)
Metric fasteners use a two-number system (e.g., 8.8, 10.9) stamped on the head. First number × 100 = tensile strength in MPa. Multiply both numbers × 10 = yield strength.
| Class | Tensile Strength | Yield Strength | SAE Equivalent | Head Marking | Best For |
|---|---|---|---|---|---|
| 4.6 | 400 MPa (58 ksi) | 240 MPa | Grade 2 | "4.6" | Low-stress, general purpose |
| 8.8 | 800 MPa (116 ksi) | 640 MPa | ≈ Grade 5 | "8.8" | Automotive, machinery, most industrial |
| 10.9 | 1,040 MPa (150 ksi) | 940 MPa | ≈ Grade 8 | "10.9" | High-stress, heavy equipment |
| 12.9 | 1,220 MPa (177 ksi) | 1,100 MPa | > Grade 8 | "12.9" | Maximum strength, aerospace |
Quick Reference: Class 8.8 ≈ Grade 5 | Class 10.9 ≈ Grade 8
Stainless Steel
| Alloy | Composition | Tensile Strength | Corrosion | Magnetic | Best For |
|---|---|---|---|---|---|
| 18-8 / 304 | 18% Cr, 8% Ni | 75,000–100,000 PSI | Excellent | Slightly | General corrosion resistance, food, architectural |
| 316 | 16% Cr, 10% Ni, 2% Mo | 75,000–100,000 PSI | Superior | No | Marine, chemical processing, saltwater exposure |
| 410 | 12% Cr | 110,000+ PSI | Moderate | Yes | Heat-treatable, wear resistance, valves |
| 17-4 PH | 17% Cr, 4% Ni | 130,000–190,000 PSI | Good | Yes | Aerospace, high-strength + corrosion resistance |
Stainless Steel Property Classes (ISO 3506-1)
Stainless fasteners use an alphanumeric system: A2 = 304 stainless, A4 = 316 stainless. The number indicates minimum tensile strength (÷10 = MPa).
| Class | Material | Tensile Strength | Yield Strength | Best For |
|---|---|---|---|---|
| A2-50 | 304 SS | 500 MPa (72 ksi) | 210 MPa | Soft condition, general use |
| A2-70 | 304 SS | 700 MPa (102 ksi) | 450 MPa | Cold worked, higher strength (most common) |
| A2-80 | 304 SS | 800 MPa (116 ksi) | 600 MPa | Heavily worked, max strength |
| A4-50 | 316 SS | 500 MPa (72 ksi) | 210 MPa | Marine, soft condition |
| A4-70 | 316 SS | 700 MPa (102 ksi) | 450 MPa | Marine, higher strength (most common marine) |
| A4-80 | 316 SS | 800 MPa (116 ksi) | 600 MPa | Marine, maximum strength |
Key Difference: A2 (304) for general corrosion resistance. A4 (316) for marine/chloride environments. Learn more →
Common Coatings & Platings
| Coating | Salt Spray Hours | Appearance | RoHS | Torque Effect | Notes |
|---|---|---|---|---|---|
| Zinc Clear | 8–24 hrs | Silver/bright | Yes | Standard | Most common, general indoor use |
| Zinc Yellow | 72–96 hrs | Gold/yellow | Yes | Standard | Better corrosion than clear zinc |
| Black Oxide | 0–2 hrs | Black matte | Yes | Reduced friction | Aesthetics, oil retention, minimal protection |
| Black Phosphate | 4–8 hrs | Dark gray/black | Yes | Reduced friction | Drywall screws, interior use |
| Hot-Dip Galvanized | 500+ hrs | Dull gray, rough | Yes | Higher friction | Outdoor structural, bridges, utilities |
| Dacromet / Geomet | 500–1,000 hrs | Silver gray | Yes | Consistent | Automotive, no hydrogen embrittlement |
| Cadmium | 250–500 hrs | Silver | No | Low friction | Aerospace, mil-spec (being phased out) |
| Nickel | 100+ hrs | Bright silver | Yes | Standard | Decorative, moderate corrosion resistance |
| Chrome | 100–250 hrs | Mirror bright | Varies | Standard | Decorative, hard wear surface |
Zinc Flake Coatings (Automotive OEM Standard)
Zinc flake coatings provide superior corrosion protection without hydrogen embrittlement risk — ideal for high-strength fasteners.
| Coating | Salt Spray Hours | Appearance | H.E. Risk | Best For |
|---|---|---|---|---|
| Dacromet | 500–720 hrs | Silver-gray matte | None | Automotive, Grade 10.9+ bolts |
| Geomet | 720–1,000 hrs | Silver-gray matte | None | Automotive underbody, chassis |
| Magni 565 | 1,000+ hrs | Dark gray/black | None | Severe underbody, wheel bolts |
| Delta-Protekt | 720–1,000 hrs | Silver or black | None | European OEM, structural |
Why Zinc Flake? No hydrogen embrittlement — safe for Grade 8, 10.9, 12.9. 10–20× better corrosion than electroplated zinc. Consistent torque-tension. RoHS/REACH compliant.
Specialty Materials
Silicon Bronze
95% copper + silicon. Excellent saltwater corrosion resistance. Non-sparking, non-magnetic. Ideal for marine, wood boat building, and electrical applications. Stronger than brass.
Brass
Copper-zinc alloy. Good corrosion resistance, non-sparking, electrically conductive. Lower strength than steel. Used in plumbing, electrical, and decorative applications.
Nylon
Lightweight, non-conductive, non-magnetic, chemically resistant. Low strength compared to metals. Used in electronics, electrical insulation, and applications requiring non-conductivity.
Aluminum
Lightweight (1/3 the weight of steel), good corrosion resistance, non-magnetic. Lower strength. Used in aerospace, electronics, and weight-sensitive applications.
Titanium
60% lighter than steel with comparable strength. Excellent corrosion resistance — outperforms 316SS in many environments. Non-magnetic. Used in aerospace, motorsports, medical implants. 10–20× steel pricing.
Related Technical Resources
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