Metric Stainless Steel Bolt Strength Chart (Class 50, 70, 80, 100) | Monster Bolts
This guide focuses on stainless steel metric bolt classes—A2-50, A2-70, A4-80, and Class 100—what their head markings mean, and how their yield and tensile strength compare. We also include quick US/SAE context and a printable PDF.
Download: Printable Stainless Steel Strength Chart (PDF)
Key terms (quick definitions)
- Proof load: maximum axial load a bolt can withstand without permanent set (often “N/A” for stainless classes).
- Yield strength: stress where permanent deformation begins.
- Tensile strength: minimum ultimate stress before fracture.
- Conversion: 1 MPa = 1 N/mm² ≈ 145 PSI.
Stainless Steel Classes & Mechanical Properties
Values below reflect the commonly used minimums for popular stainless classes. Always verify against your specific standard and drawing.
| Head Marking | Metric Class | Proof Load (MPa) |
Min Yield (MPa) |
Min Tensile (MPa) |
Notes |
|---|---|---|---|---|---|
 |
Class 100 | — | 800 | 1,000 | Strongest stainless here; uncommon in the market. |
 |
A4-80 (SS) | N/A | 600 | 800 | ≈316 stainless; marine/corrosive environments. |
 |
A2-70 (SS) | N/A | 450 | 700 | ≈304 / 18-8; most common stainless class. |
 |
A2-50 (SS) | N/A | 210 | 500 | As-formed (soft). Not cold-worked for higher strength. |
About “equivalents” (US vs Metric)
US/SAE grades (e.g., Grade 8, Grade 5, Grade 2) and metric classes use different systems. Numbers may look similar, but they are not strict 1:1 equivalents. For mixed benches, these typical minimum tensile strengths are often cited for context:
| US / SAE Grade | Min Tensile (PSI) | Approx (MPa) | Closest Stainless Class (context only) |
|---|---|---|---|
| Grade 8 | 150,000 | ≈ 1,034 | (None direct) |
| Grade 5 | 120,000 | ≈ 827 | A4-80 (context) |
| Grade 2 | 74,000 | ≈ 510 | A2-50 (context) |
Practical notes
- Corrosion: A4 (≈316) offers better chloride resistance than A2 (≈304).
- Galling risk: stainless-to-stainless threads can seize; use anti-seize and proper speed. See our guide on thread galling prevention.
- Magnetism: cold-worked stainless (e.g., A2-70) can show slight magnetism—normal and not a defect.
- Torque: always follow the drawing/spec; for socket screws see our Metric Socket Screw Torque Chart.
Related charts & tools:
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