Home » ISO 7380 Button Head Socket Cap Screw A4 Stainless

ISO 7380 Button Head Socket Cap Screw A4 Stainless

FULLERKREG ISO 7380-1 A4 Marine Stainless Steel Button Head Socket Cap Screws

FULLERKREG ISO 7380-1 A4 Marine Stainless Steel Button Head Socket Cap Screws are premium corrosion-resistant fasteners featuring a low-profile dome-shaped button head with a hexagon socket drive. Manufactured from A4 (SUS316) austenitic stainless steel with a passivated natural finish, these screws combine the clean aesthetic of the button head design with the superior corrosion resistance of marine-grade stainless steel. 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.

Product Specifications

  • Standard: ISO 7380-1
  • Material: A4 Marine Stainless Steel (SUS316 / 316 SS)
  • Strength Grade: A4-70
  • Tensile Strength: Min. 700 MPa
  • Proof Load Stress (Rp0.2): Min. 450 MPa
  • Hardness: ≤95 HRB (max. 210 HV)
  • Head Type: Button head (low-profile dome)
  • Surface Treatment: Passivation — natural silver finish (pickling & passivation)
  • Thread Type: Metric coarse, full thread
  • Thread Tolerance: 6g
  • Drive Type: Hexagon socket (Allen key / hex key)
  • Sizes Available: M3 – M16

Why A4 (SUS316) vs A2 (SUS304)?

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

Material — A4 Marine Stainless Steel (SUS316) Chemical Composition (%)

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

Mechanical Properties — A4-70 (ISO 7380-1)

Per ISO 3506-1 requirements for A4-70 stainless steel fasteners.

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) —

Key Features

  • Low-profile button head — smooth dome design, approximately 50% lower than standard socket cap screws, ideal for aesthetic and space-constrained applications
  • Wide bearing surface — larger head diameter distributes load over a greater area, reducing pull-through risk in soft or thin materials
  • A4 Marine Stainless Steel (SUS316) — the highest corrosion resistance among standard stainless steel fastener grades
  • Molybdenum-enhanced alloy — 2–3% Mo content provides outstanding pitting and crevice corrosion resistance in chloride environments
  • Passivated natural finish — clean silver appearance with enhanced oxide layer for maximum rust resistance
  • Non-magnetic — suitable for applications sensitive to magnetic interference
  • Hygienic & food-safe — compliant for food processing, pharmaceutical, and medical equipment use
  • RoHS & REACH compliant — no restricted hazardous substances
  • ISO/TS16949 quality management — hardness test, tensile test, and PPAP report available on request

Applications

FULLERKREG ISO 7380-1 A4 marine stainless steel button head socket cap screws are widely used in demanding corrosive environments:

  • Marine vessels, boat fittings, and dock structures
  • Offshore platforms and coastal architectural hardware
  • Desalination and water treatment equipment
  • Chemical processing and petrochemical plants
  • Food and beverage processing machinery
  • Pharmaceutical and medical device manufacturing
  • Swimming pools, aquatic facilities, and spa equipment
  • Outdoor signage and architectural panels in coastal areas
  • Any application where A2 (SUS304) is insufficient due to chloride or acid exposure

Corrosion Resistance Guide — A4 (SUS316)

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

Dimensional Specifications — ISO 7380-1 (Unit: mm)

Thread (d) Pitch (p) Head Dia. dk Max. Head Dia. dk Min. Head Height k Max. Head Height k Min. Key Size s Key Depth t Min. Body Dia. ds Max. Body Dia. ds Min.
M3 0.5 5.70 5.50 1.65 1.35 2.0 0.74 3.00 2.86
M4 0.7 7.60 7.36 2.20 1.80 2.5 1.05 4.00 3.82
M5 0.8 9.50 9.22 2.75 2.25 3.0 1.35 5.00 4.82
M6 1.0 10.50 10.22 3.30 2.70 4.0 1.60 6.00 5.82
M8 1.25 14.00 13.57 4.40 3.60 5.0 2.20 8.00 7.78
M10 1.5 17.50 17.05 5.50 4.50 6.0 2.75 10.00 9.78
M12 1.75 21.00 20.48 6.60 5.40 8.0 3.30 12.00 11.73
M16 2.0 28.00 27.48 8.80 7.20 10.0 4.40 16.00 15.73

Frequently Asked Questions

Q: What is the difference between ISO 7380-1 and ISO 7380-2?
ISO 7380-1 is the standard button head socket cap screw with a plain button head. ISO 7380-2 features a button head with a flange (wider bearing surface). This page covers ISO 7380-1 (no flange).

Q: Why choose A4 over A2 for 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: Can button head screws handle the same torque as socket cap screws?
No. Due to the shallower socket depth in the button head, the maximum recommended tightening torque is lower than for standard socket cap screws (DIN 912). Button head screws are not recommended for high-torque structural joints.

Q: Are A4 button head screws magnetic?
A4 stainless steel is generally non-magnetic in the annealed state. Cold working during manufacturing may induce slight magnetism. For strictly non-magnetic applications, please confirm with our technical team.

Q: Can I get material certificates and test reports?
Yes. PPAP reports, material certificates (mill certificates with Mo content verification), hardness test reports, and tensile test reports are available upon request.

Packaging & Availability

  • Standard sizes M3 – M16 available in stock
  • Bulk carton packaging; custom packaging available
  • Material certificates (including Mo content verification) available on request
  • Custom lengths accepted for large orders

Download Specification

Quality Assurance

All FULLERKREG ISO 7380-1 A4 marine stainless steel button head socket cap screws are manufactured under strict quality control procedures including:

  • Hardness test (≤95 HRB)
  • Tensile strength test (min. 700 MPa)
  • Dimensional inspection per ISO 7380-1
  • Chemical composition verification (SUS316, Mo content confirmed)
  • Salt spray corrosion test
  • PPAP documentation available upon request

For wholesale pricing, bulk orders, material certificates, or technical inquiries, please contact our sales team.

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