ENGINEERING DOSSIER Reading Time: 5 min • Updated: 2026-09-19

Stainless Fastener Engineering: Grade A2 (AISI 304) vs Grade A4 (AISI 316) Selection

Engineering guide for selecting structural bolts, T-bolts, spring channel nuts, and serrated flange nuts in photovoltaic mounting systems.

Lead Author: Celalettin YAGMAHAN (Civil Engineer & Structural Lead)

Key Engineering Takeaways

✓ A2-70 is the worldwide standard for commercial inland solar installations
✓ A4-70 / A4-80 with molybdenum is mandatory for coastal and floating PV projects
✓ All SolarAlu fasteners feature serrated flange nuts that resist dynamic wind loosening

Austenitic Stainless Metallurgy & Tensile Classes

Grade A2 (AISI 304, 1.4301) contains 18% chromium and 8% nickel, providing excellent corrosion resistance in continental and urban atmospheres. Grade A4 (AISI 316, 1.4401) adds 2-3% molybdenum, significantly inhibiting pitting and crevice corrosion in chloride-rich coastal and marine environments. The '-70' designation denotes minimum 700 MPa ultimate tensile strength.

When is Grade A4 Mandatory?

For solar plants installed within 5 kilometers of the coastline, on floating water reservoirs, or near chemical/fertilizer plants, Grade A4 fasteners are required to avoid pitting stress cracking.

TECHNICAL QUESTIONS

Frequently Asked Technical Questions

Why shouldn't zinc-plated steel bolts be used with aluminum rails?

Standard zinc plating erodes in outdoor conditions within 2–5 years, resulting in severe red rust and frozen threads.

Do you provide certificate of compliance for fasteners?

Yes, our fasteners come with EN 10204 3.1 material test certificates verifying chemical composition and tensile limits.

STRUCTURAL STATICS DESK

Require Project Statics Calculation?

Our engineering desk calculates project-specific wind uplift and snow load moment capacities according to Eurocode 9 within 24 hours.

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