304 - Stainless Steel - Serrated - Hexagon flange bolt

Technical Performance of SS304 Flange Bolts

Grade 304, often designated as "A2" in the fastener industry, is the workhorse of stainless steel bolts. It contains approximately 18% chromium and 8% nickel, which forms a passive oxide layer that protects the steel from rust. When combined with the serrated flange design, it becomes a high-utility fastener that speeds up assembly time while ensuring joint security.

Mechanical Properties (A2-70)

Most of our 304 flange bolts are manufactured to the A2-70 strength class standard:

• "A2" Designation: Refers to the austenitic steel group 304. It is non-magnetic in its raw state but may become slightly magnetic after the cold-forging process used to make the bolt.
• "70" Designation: Indicates the tensile strength class.
  • Tensile Strength: Minimum 700 N/mm². This means the bolt can withstand significant pulling force without breaking.
  • Yield Strength: Minimum 450 N/mm². This is the limit to which the bolt can be tightened before it permanently stretches.
• Hardness: The cold working process hardens the surface, allowing the serrations to effectively grip into softer metals like aluminum or mild steel.

Quality Assurance

We ensure our A2-70 fasteners meet strict chemical and mechanical standards. An EN 10204 3.1 Material Certificate verifying the chemical composition is available upon request. Please note that third-party inspection services require an additional fee.

Ideal Applications for SS304

These serrated flange bolts are optimized for environments where rust protection is needed but extreme chemical resistance (like 316) is unnecessary:

• Solar PV Installations: Fastening aluminum rails and clamps (SS304 is compatible with aluminum and resists outdoor weather).
• Automotive Parts: Securing bumpers, headlights, and under-hood components where vibration is an issue.
• General Construction: Outdoor timber connections, fencing, and signage.
• Food Processing: Machinery components in non-corrosive zones (wash-down areas usually require 316).

Frequently Asked Questions

Can I use SS304 flange bolts near the ocean?

For direct coastal environments (within 5km of the sea), SS304 is not recommended as it can develop "tea staining" (surface rust) due to salt spray. For marine environments, you should upgrade to our SS316 (A4) flange bolts.

What does "galling" mean and how do I prevent it?

Stainless steel threads can sometimes seize up or "cold weld" together during tightening, known as galling. This is common with flange bolts due to the friction. To prevent this, we recommend using a low RPM when tightening with power tools and applying an anti-seize lubricant paste to the threads.

Why use a serrated flange instead of a split washer?

A serrated flange is superior for two reasons. First, it is a single integrated piece, so there is no risk of the washer splitting or falling out. Second, the serrations physically dig into the material, providing a mechanical lock that is stronger than the friction-only resistance of a split washer.