A2 and A4 fasteners are both stainless steel fasteners, but they are not selected for the same environment. The main difference is corrosion resistance.

In buyer terms, A2 is commonly used for general stainless applications. A4 is selected when chloride exposure, coastal air, or chemical contact becomes more serious.

The wrong choice may not fail during installation. It usually shows up later as staining, pitting, seized threads, or customer complaints.

What A2 and A4 Mean

Under ISO 3506, A2 and A4 refer to austenitic stainless steel fastener groups. Buyers often compare them with 304-type and 316-type stainless steel.

Buyers can review stainless steel fasteners when comparing A2 and A4 options.

When to Choose A2 Fasteners

General Industrial Use

A2 fasteners are suitable for many normal environments.

Use A2 for:

• Indoor machinery
• Electrical cabinets
• Furniture hardware
• Food equipment with mild exposure
• Clean outdoor structures
• General brackets and covers

A2 is usually easier to source and more cost-effective than A4. For standard sizes, buyers can also check standard fasteners.

When to Choose A4 Fasteners

Chloride and Harsh Exposure

A4 is the better choice when corrosion risk is higher.

Use A4 for:

• Coastal structures
• Marine equipment
• Chemical plants
• Outdoor humid environments
• Washdown equipment
• Swimming pool surroundings
• Road-salt exposure areas

A4 is not immune to corrosion, but it gives better resistance than A2 in chloride environments.

For projects where corrosion resistance is critical, compare A4 with various coated fasteners before final approval.

Common Buyer Mistakes

Avoid these problems:

• Using A2 in marine or coastal projects.
• Choosing A4 only by name without checking strength class.
• Mixing A2 bolts with A4 nuts in critical assemblies.
• Ignoring thread galling during stainless steel installation.
• Not confirming whether A2-70, A4-70, or A4-80 is required.
• Selecting stainless steel without checking the connected metal.

For high-load stainless assemblies, review high-strength fasteners and confirm mechanical requirements.

RFQ Checklist

Before ordering, provide:

1. A2 or A4 grade
2. Property class: 50, 70, or 80
3. Product type: bolt, nut, washer, screw, stud
4. Size, pitch, and length
5. Surface condition or passivation requirement
6. Application environment
7. Matching nuts and washers
8. Required inspection documents

Final Advice

Choose A2 for general stainless steel fastening. Choose A4 when corrosion resistance matters more, especially in chloride, coastal, marine, and chemical environments.

The safest RFQ defines grade, strength class, size, thread, matching parts, and working environment before production.