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

ISO 7380-1 — Full Dimensional Specification (PDF)

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.