Stainless fastener standards: A2-70, A4-80 and ASTM A193/A194
A2-70 (304-based) and A4-80 (316-based) are common stainless bolt grades; pressure and high-temperature service uses ASTM A193/A194 B8/B8M series.
Stainless fasteners use different grade designations from plate and sheet. Common ones:
• A2-70: austenitic 304-based material, 700 MPa tensile class; general corrosion environments.
• A4-80: 316-based material, 800 MPa tensile class; better for chloride or coastal environments.
• ASTM A193 B8 / B8M: stainless bolts for pressure vessels (304/316 based); B8M is the 316 series. Matching nuts are A194 8/8M.
• Others: A2-50/A4-50 (lower strength), A4-70 etc.
Selection guidance:
1) General structures and indoor environments: A2-70.
2) Coastal, chloride or chemical service: A4-80/A4-70 (316 series).
3) Pressure equipment and high-temperature flanges: follow ASME and select A193 B8/B8M + A194 8/8M, checking allowable stress at design temperature.
4) Note that strength class and material grade are two systems — do not rely on the 70/80 number alone.
Purchasing reminder: require the certificate to state material grade, strength class, standard and lot number; for high-strength bolts confirm solution annealing to avoid stress-corrosion risk from cold work.
Compiled by SteelWe editors and industry experts. For industry exchange only; not trading or investment advice. Cite the source when quoting.
