Steel grades
| Grade | Tensile strength | Marking | Notes |
|---|---|---|---|
| SAE 2 (low carbon) | 74 ksi (510 MPa) | No marking | Cheap commodity bolts |
| SAE 5 (medium-carbon, heat-treated) | 120 ksi (830 MPa) | 3 radial lines | General industrial |
| SAE 8 (alloy steel) | 150 ksi (1 040 MPa) | 6 radial lines | Automotive, high-stress |
| SAE 9 | 180 ksi (1 240 MPa) | — | Specialty fasteners |
| Metric 4.6 | 400 MPa | — | Equivalent to SAE 2 |
| Metric 8.8 | 830 MPa | "8.8" on head | Equivalent to SAE 5 |
| Metric 10.9 | 1 040 MPa | "10.9" on head | Equivalent to SAE 8 |
| Metric 12.9 | 1 220 MPa | "12.9" on head | High-strength alloy |
Stainless
| Type | Tensile (typ.) | Corrosion | Notes |
|---|---|---|---|
| 304 (18-8, A2) | 515 MPa | Good | General food / hardware |
| 316 (A4) | 515 MPa | Better (Mo) | Marine / chloride exposure |
| 316L | 485 MPa | Better | Weld-grade |
| 17-4 PH | 1 100 MPa | Good | Precipitation-hardened, high strength |
Non-ferrous
| Material | Use | Notes |
|---|---|---|
| Brass | Low-stress | Corrosion resistant, soft |
| Aluminum | Weight-critical | Much weaker than steel; galls |
| Titanium | Aerospace, high-end bikes | Strength-to-weight king; expensive |
| Monel | Marine / chemical | Very corrosion resistant |
| Nylon | Insulating / electronic | Low strength |
Coatings
| Zinc plated | Cheap, mild corrosion protection, not for outdoor |
|---|---|
| Hot-dip galv. | Thick zinc layer, outdoor construction |
| Black oxide | Cosmetic, minor corrosion resistance |
| Cadmium | Aerospace (legacy, toxic) |
| PTFE | Low friction, chemical resistance |
Notes
- Galvanic corrosion: avoid direct contact between dissimilar metals (aluminum + steel screws fail fast outdoors without isolation).
- Grade 8 fasteners are brittle — prefer grade 5 for shock / fatigue loading.
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