Technical Guide
A2 vs A4 Stainless Steel Fasteners
A2 and A4 are the two stainless steel fastener grades most commonly specified in industrial and marine work. The letter refers to the base steel; the number after the dash (50 or 70) refers to the property class, not the material.
The material difference
A2 fasteners are made from austenitic stainless steel equivalent to grade 304 — chromium-nickel steel with good general corrosion resistance.
A4 fasteners are made from steel equivalent to grade 316, which adds molybdenum to the alloy. Molybdenum improves resistance to chlorides — the corrosion that comes from salt water, de-icing salts, and some industrial chemicals.
A2 vs A4 at a glance
| A2 | A4 | |
|---|---|---|
| Base steel | 304-equivalent (Cr-Ni) | 316-equivalent (Cr-Ni-Mo) |
| Molybdenum added | No | Yes |
| Typical environment | Indoor, dry/general outdoor use | Marine, coastal, chloride/chemical exposure |
| Property classes stocked | A2-50, A2-70 | A4-50, A4-70 |
What the -50 / -70 means
The number after the grade (50 or 70) is the property class — it describes the bolt's strength, not the steel composition. A2-70/A4-70 is the higher-strength property class within each grade; A2-50/A4-50 is the standard class. A2-70 and A4-70 are not stronger by virtue of the A4 material — the 316 alloy is chosen for corrosion resistance, and the property class is a separate strength specification within each material.
Kesharia's verified A2/A4 range
Kesharia stocks A2-50, A2-70, A4-50 and A4-70 hex bolts from M6 to M64 (metric) and 1/4" to 2-1/2" (imperial), passivated to ASTM A380, supplied to DIN 931/933/601/558/960/961/7990, ISO 4014–4017, ASME B18.2.1 and AS 1390 depending on size.
Frequently Asked Questions
Is A4 always better than A2?
Not universally — A4 is the better choice specifically where chloride exposure (marine, coastal, some washdown/chemical environments) is a factor. For general indoor or dry-outdoor use, A2 is normally sufficient and is the more commonly stocked grade.
Does A4 mean a stronger bolt?
No — strength is set by the property class (-50 or -70), not by A2 vs A4. A4-70 and A2-70 share the same property class; the A4 designation is about corrosion resistance, not strength.
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