Flanged Hexagon Bolts (DIN 6921) — Marine Stainless Steel A4 (SUS316) | FULLERKREG

FULLERKREG DIN 6921 Flanged Hexagon Bolts are precision-engineered fasteners combining a standard hexagon head with an integrated load-distributing flange. Manufactured from A4 marine-grade stainless steel (SUS316) to strength class A4-70, these bolts deliver outstanding corrosion resistance in the most demanding environments — including offshore, marine, chemical processing, and coastal construction applications.

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Two Flange Head Variants

This collection offers both standard configurations as defined by DIN 6921:

• Non-Serrated Flanged (Smooth Flange) — A flat, smooth bearing surface beneath the head. Ideal for applications requiring easy disassembly, use with soft or coated surfaces, or where flange serrations could damage the mating material. Provides uniform load distribution without surface marking.
• Serrated Flanged — Features radial serrations on the underside of the flange that bite into the mating surface upon tightening. This mechanical locking action significantly improves vibration resistance and prevents self-loosening, making it the preferred choice for dynamic load applications, automotive, and machinery assemblies.

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Material & Grade Specification

Property	Specification
Material Grade	A4 (SUS316 / 1.4401)
Strength Class	A4-70
Min. Tensile Strength	700 MPa
Min. 0.2% Proof Stress	450 MPa
Min. Elongation	20%
Hardness (max.)	220 HV
Chromium Content	16.0–18.5%
Nickel Content	10.0–14.0%
Molybdenum Content	2.0–3.0%
Surface Finish	Natural / Passivated

The addition of 2–3% molybdenum in A4/SUS316 provides superior resistance to chloride-induced pitting and crevice corrosion compared to standard A2/SUS304 — making it the material of choice for marine, coastal, and chemical environments.

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Dimensional Standards — DIN 6921

All FULLERKREG DIN 6921 bolts are manufactured and inspected in full conformance with the DIN 6921 dimensional standard and DIN 267-11 for mechanical properties of stainless steel fasteners.

Thread Size	Pitch (mm)	Width Across Flats s (mm)	Flange Diameter dc (mm)	Head Height k (mm)	Wrench Size
M5	0.8	8	14.2	3.5	8 mm
M6	1.0	10	17.0	4.0	10 mm
M8	1.25	13	22.0	5.5	13 mm
M10	1.5	15 (16)	27.0	6.5	15/16 mm
M12	1.75	18	32.0	8.0	18 mm
M14	2.0	21	37.0	9.0	21 mm
M16	2.0	24	43.0	10.0	24 mm
M20	2.5	30	53.0	12.5	30 mm

All threads are metric coarse per ISO 261 / DIN 13. Tolerances per ISO 4759-1, property class 6g for external threads.

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Key Features & Benefits

• Integrated Flange: Eliminates the need for a separate washer — the built-in flange distributes clamping load over a larger bearing area, reducing surface pressure and the risk of joint relaxation.
• Marine-Grade Corrosion Resistance: A4 (SUS316) with molybdenum resists saltwater, chlorides, acids, and industrial chemicals far beyond standard stainless grades.
• A4-70 Strength: Higher proof load than standard A4-50, suitable for structurally demanding connections without sacrificing corrosion performance.
• Vibration Resistance (Serrated variant): Serrated flange underside locks against the mating surface, preventing loosening under dynamic or cyclic loads.
• Non-Magnetic: Austenitic SUS316 is essentially non-magnetic in the annealed condition — suitable for sensitive electronic or instrumentation environments.
• Hygienic & Low-Maintenance: Passivated surface is easy to clean and does not require painting, plating, or ongoing corrosion treatment.
• Full DIN 6921 Compliance: Manufactured to exact dimensional and mechanical property requirements for interchangeability and engineering confidence.

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Typical Applications

• Marine & offshore structures, boat fittings, dock hardware
• Coastal and waterfront construction
• Chemical processing plants and pipework flanges
• Food processing and pharmaceutical equipment
• Automotive and heavy machinery (serrated variant for vibration resistance)
• HVAC, plumbing, and water treatment systems
• Architectural metalwork in corrosive environments
• Electrical enclosures and instrumentation panels

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Standards & Compliance

• DIN 6921 — Hexagon bolts with flange (dimensional standard)
• DIN 267-11 / ISO 3506-1 — Mechanical properties of stainless steel bolts and screws
• ISO 261 — Metric thread series
• ISO 4759-1 — Tolerances for fasteners
• EN ISO 898-1 — Reference standard for mechanical properties (informational context for property class marking)

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Corrosion Resistance Comparison

Environment	A2 (SUS304)	A4 (SUS316) — This Product
Fresh water	✓ Excellent	✓ Excellent
Mild atmospheric	✓ Excellent	✓ Excellent
Coastal / salt air	△ Moderate	✓ Excellent
Seawater / marine immersion	✗ Limited	✓ Good
Chloride solutions	✗ Poor	✓ Good
Dilute acids	△ Moderate	✓ Good
Chemical processing	✗ Not recommended	✓ Suitable

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Marking & Identification

In accordance with DIN 267-11 and ISO 3506-1, FULLERKREG DIN 6921 A4-70 bolts are marked on the head with:

• A4-70 — Material and strength class designation
• FULLERKREG manufacturer mark — Traceable to production batch

Marking may be omitted on sizes below M5 where head geometry does not permit legible stamping.

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Packaging & Supply

• Available in standard retail packs, bulk bags, and full-box quantities
• Each pack clearly labeled with: Part number, Thread size, Length, Material grade (A4-70), Standard (DIN 6921), and Flange type (Serrated / Non-Serrated)
• Custom packaging and private-label options available for wholesale and OEM customers
• Certificates of conformance (CoC) and material test reports (MTR) available on request

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Frequently Asked Questions

Q: What is the difference between A4-70 and A4-80?
A: A4-70 has a minimum tensile strength of 700 MPa and proof stress of 450 MPa. A4-80 offers higher strength (800 MPa / 640 MPa) but is less commonly stocked. For most marine and structural applications, A4-70 provides an excellent balance of strength and corrosion resistance. FULLERKREG supplies A4-70 as the standard grade for DIN 6921.

Q: Can I use these bolts in direct seawater immersion?
A: A4 (SUS316) performs well in seawater and marine splash zones. For prolonged full immersion in stagnant seawater or high-chloride environments, additional engineering assessment is recommended. Crevice corrosion risk should be considered in tight joints.

Q: Do I need a washer with a flanged bolt?
A: Generally no — the integrated flange acts as a built-in washer, distributing load and protecting the mating surface. However, a separate washer may still be used on very soft materials or where surface protection is critical.

Q: Which variant should I choose — serrated or non-serrated?
A: Choose serrated when vibration resistance and self-locking are priorities (machinery, automotive, dynamic loads). Choose non-serrated when easy disassembly, surface protection, or use with soft/coated materials is required.

Q: Are these RoHS and REACH compliant?
A: Yes. FULLERKREG A4 stainless steel fasteners do not contain restricted substances under RoHS or REACH regulations. Documentation available on request.

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FULLERKREG — Precision Fasteners for Demanding Environments. All products manufactured and inspected to international standards. For technical support, custom specifications, or volume pricing, please contact our sales team.