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FULLERKREG ISO 7380-2 A4 Marine Stainless Steel Flanged Button Head Socket Cap Screws are premium corrosion-resistant fasteners featuring a low-profile dome-shaped button head with an integrated flange and a hexagon socket drive. Manufactured from A4 (SUS316) austenitic stainless steel with a passivated natural finish, these screws combine the superior corrosion resistance of marine-grade stainless steel with the engineering advantages of an integrated flange. The addition of 2–3% molybdenum (Mo) in SUS316 provides dramatically better resistance to chlorides, saltwater, and acids compared to A2 (SUS304), making these the definitive choice for marine, coastal, chemical, and food processing environments where both corrosion resistance and pull-through resistance are required.
The molybdenum content in A4 is the critical differentiator for corrosive environments:
| Property | A2 (SUS304) | A4 (SUS316) — This Page |
|---|---|---|
| Chromium (Cr) | 18–20% | 16–18% |
| Nickel (Ni) | 8–10.5% | 10–14% |
| Molybdenum (Mo) | None | 2–3% (key advantage) |
| Chloride resistance | Good | Excellent |
| Saltwater / marine | Limited | Superior — recommended grade |
| Acid resistance | Moderate | Superior |
| Pitting corrosion resistance | Standard | Significantly better |
| Price point | Standard | Premium |
| Property | ISO 7380-2 Flanged (This Page) | ISO 7380-1 Plain Button Head |
|---|---|---|
| Head profile | Low dome + integrated flange | Low dome only |
| Bearing surface area | Significantly larger (flange) | Standard button head |
| Washer required? | No — flange acts as integrated washer | Sometimes yes |
| Pull-through resistance | Superior | Standard |
| Load distribution | Excellent on thin/soft materials | Good |
| Assembly efficiency | Faster — one fewer component | Standard |
| Best for | Thin panels, soft materials, high pull-through risk | General low-profile applications |
All values are maximum unless a range is indicated.
| Grade | C (max) | Si (max) | Mn (max) | P (max) | S (max) | Cr | Ni | Mo |
|---|---|---|---|---|---|---|---|---|
| SUS316 (A4) | ≤0.08 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 16.00–18.00 | 10.00–14.00 | 2.00–3.00 |
| Property | Requirement | Unit |
|---|---|---|
| Tensile Strength (Rm) | Min. 700 | MPa |
| Proof Load Stress (Rp0.2) | Min. 450 | MPa |
| Hardness (max) | ≤95 HRB / ≤210 HV | HRB / HV |
| Elongation after fracture (A) | Min. 25 | % |
| Thread Tolerance Class | 6g | — |
| Surface Treatment | Passivation (natural finish) | — |
| Environment | A4 (SUS316) Performance | Recommendation |
|---|---|---|
| Indoor / dry environments | Excellent | ✅ Ideal |
| Outdoor / atmospheric exposure | Excellent | ✅ Ideal |
| Marine / saltwater (direct) | Very good | ✅ Recommended grade |
| Offshore / coastal structures | Very good | ✅ Recommended grade |
| Food & pharmaceutical processing | Excellent | ✅ Ideal |
| Chemical processing (mild acids) | Very good | ✅ Suitable |
| Chloride-rich environments | Very good | ✅ Recommended grade |
| Swimming pools / aquatic facilities | Very good | ✅ Recommended grade |
| Strong oxidizing acids | Moderate | ⚠️ Consult technical team |
FULLERKREG ISO 7380-2 A4 marine stainless steel flanged button head socket cap screws are widely used in demanding corrosive environments:
Key dimensions per ISO 7380-2 (2022). The flange diameter (dc) is the critical additional dimension vs. ISO 7380-1.
| Thread (d) | Pitch (p) | Head Dia. dk Max. | Head Dia. dk Min. | Flange Dia. dc Max. | Flange Dia. dc Min. | Head Height k Max. | Head Height k Min. | Key Size s | Key Depth t Min. |
|---|---|---|---|---|---|---|---|---|---|
| M4 | 0.7 | 7.60 | 7.36 | 9.40 | 9.00 | 2.20 | 1.80 | 2.5 | 1.05 |
| M5 | 0.8 | 9.50 | 9.22 | 11.80 | 11.40 | 2.75 | 2.25 | 3.0 | 1.35 |
| M6 | 1.0 | 10.50 | 10.22 | 13.60 | 13.20 | 3.30 | 2.70 | 4.0 | 1.60 |
| M8 | 1.25 | 14.00 | 13.57 | 17.90 | 17.50 | 4.40 | 3.60 | 5.0 | 2.20 |
| M10 | 1.5 | 17.50 | 17.05 | 22.30 | 21.80 | 5.50 | 4.50 | 6.0 | 2.75 |
| M12 | 1.75 | 21.00 | 20.48 | 26.70 | 26.20 | 6.60 | 5.40 | 8.0 | 3.30 |
| M16 | 2.0 | 28.00 | 27.48 | 35.70 | 35.20 | 8.80 | 7.20 | 10.0 | 4.40 |
Q: What is the difference between ISO 7380-1 and ISO 7380-2?
ISO 7380-1 is the plain button head socket cap screw with no flange. ISO 7380-2 adds an integrated flange under the button head, which significantly increases the bearing surface area, acts as a built-in washer, and provides superior pull-through resistance.
Q: Why choose A4 over A2 for flanged button head screws?
If your application involves saltwater, marine environments, chloride exposure, or aggressive chemicals, A4 (SUS316) is the correct choice. The 2–3% molybdenum content in A4 provides significantly better pitting corrosion resistance than A2 (SUS304).
Q: What does A4-070 mean?
A4-070 is the property class designation per ISO 3506-1 for stainless steel fasteners. “A4” refers to the austenitic stainless steel grade (SUS316), and “070” indicates a minimum tensile strength of 700 MPa. This is equivalent to the commonly used designation A4-70.
Q: Do I still need a washer with ISO 7380-2 flanged button head screws?
In most applications, no. The integrated flange provides sufficient bearing area to replace a standard flat washer, reducing part count and assembly time.
Q: Can I get material certificates and test reports?
Yes. PPAP reports, material certificates (including Mo content verification), hardness test reports, and tensile test reports are available upon request for all FULLERKREG products.
All FULLERKREG ISO 7380-2 A4 marine stainless steel flanged button head socket cap screws are manufactured under strict quality control procedures including:
For wholesale pricing, bulk orders, material certificates, or technical inquiries, please contact our sales team.
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