A4 Stainless Steel Bolts (SS316) are a critical component in industrial fastening. They offer strong corrosion resistance. This makes them suitable for marine, chemical, and petrochemical applications.
Order Execution – Packaging That Delivers Efficiency
We recently fulfilled an A4 bolt order for a long-term Kazakh client. Specifications ranged from M16 to M22. Quantities were large. Each set included:
1 bolt
2 locknuts
2 flat washers
The client’s key requirement? Ready-to-use upon arrival. No secondary counting. No sorting delays.
Our packaging solution:
Sealed plastic bags by size – each bag labeled with dimensions and item name. No mixing.
Labeled cartons with unique numbers – each matches the packing list. Fast verification.
All cartons in custom wooden crates – secure for long-distance shipping. No damage. No loose parts.
Client feedback confirmed: on-site sorting time reduced significantly. Work efficiency improved.
No order is too small for attention to detail. Reliable delivery is our commitment.
A4 Stainless Steel Bolts Material & Property
A4 stainless steel = 316 stainless steel (SS316).
Per ISO 3506:
“A” = Austenitic stainless steel.
“4” = Chemical composition group.
Compared to A2 (304 stainless steel) , A4 contains:
Molybdenum (Mo) – approx. 2–3%.
Higher nickel (Ni) content.
These elements boost corrosion resistance, especially against chlorides.
Common property grades for A4 Stainless Steel Bolts
| Grade | Tensile Strength (MPa) | Typical Use |
| A4-70 | ≥700 | General industrial & structural connections |
| A4-80 | ≥800 | High-strength critical joints |
Choose A4-80 for higher load requirements.
A4 vs. A2 – Key Differences
A2 and A4 are the two most common stainless fastener materials. Their differences matter.
| Comparison | A2 (SS304) | A4 (SS316) |
| Key Elements | Cr ~18%, Ni ~8% | Cr ~17%, Ni ~10%, Mo ~2–3% |
| Pitting Resistance | Moderate | High (Mo enhances resistance) |
| Chloride Resistance | Limited. Corrodes in saline environments. | Good. Suitable for seawater & de-icing salts. |
| Magnetism after Cold Work | Possible | Lower tendency (more stable austenite) |
| Recommended Environment | Indoor, general atmosphere, freshwater | Marine, chemical, humid, or polluted areas |
Bottom line:
A2 works for most general uses.
A4 is an upgrade for aggressive corrosive conditions.
Appearance differences? Mostly finishing. Not chromium content. In fact, 316 has slightly lower Cr (16–18%) than 304 (18–20%).
Performance Advantages & Application Scenarios
A4’s strength is corrosion resistance – against air, moisture, acids, alkalis, and solvents.
Typical industries:
| Application | Environment | Why A4? |
| Marine & Shipbuilding | Seawater, high salt spray | Resists chloride pitting. Longer service life. |
| Chemical Plants | Acids, alkalis, solvents | Chemical resistance ensures safety. |
| Food Processing | Wet, frequent washing | Corrosion-resistant & hygienic. |
| Medical Devices | Sterilization, body fluids | Good biocompatibility. |
| Coastal Infrastructure | Humid, salt-laden air | Prevents rust-induced failures. |
Carbon steel bolts would fail quickly in these settings. A4 maintains stable connections.
Additionally, austenitic stainless steel offers:
Stable microstructure across temperatures.
No phase transformation under normal conditions.
Good ductility – reliable under complex stresses.
Installation – Avoid Galling
Stainless steel bolts are prone to thread galling (seizure) . This is inherent to austenitic grades. Excessive friction causes surface adhesion. Disassembly becomes difficult.
Preventive measures:
Apply lubricant or anti-seize compound on threads.
Control speed and torque during installation.
Summary
A4 stainless steel bolts (316/UNS S31600) outperform A2 in corrosion resistance. The molybdenum addition makes them reliable in:
Marine
Chemical
Medical
Coastal environments
For selection, consider both:
Material (A4 vs. A2)
Property grade (A4-70 vs. A4-80)
Follow proper installation practices for safe, durable connections.
Looking for a reliable stainless steel fastener supplier?
Contact us for technical support or a quote.