Home » DIN 6921 Flanged Hexagon Bolts | A2 Stainless Steel (SUS304) | Plain & Serrated Flange

DIN 6921 Flanged Hexagon Bolts | A2 Stainless Steel (SUS304) | Plain & Serrated Flange

FULLERKREG DIN 6921 Flanged Hexagon Bolts — A2 Stainless Steel (SUS304) | A2-70 | Plain & Serrated Flange

FULLERKREG DIN 6921 flanged hexagon bolts are metric hex bolts with an integrated flange beneath the hex head that acts as a built-in washer, distributing the clamping load over a larger bearing area without the need for a separate washer. Available in two flange variants:

  • Plain (Non-Serrated) Flange — smooth flange underside; standard load distribution; suitable for surfaces that must not be marked
  • Serrated Flange — knurled/serrated flange underside; bites into the mating surface under torque to provide mechanical anti-loosening resistance; preferred for vibration-prone assemblies

Manufactured from A2 stainless steel (SUS304 / 1.4301) to property class A2-70, these bolts offer excellent corrosion resistance, good mechanical strength, and a clean natural finish — suitable for food processing, architectural, marine (sheltered), and general industrial applications.

Key Features

  • Standard: DIN 6921 — Hexagon bolts with flange
  • Material: A2 Stainless Steel (SUS304 / 1.4301) — austenitic, non-magnetic in annealed state
  • Property Class: A2-70 (per ISO 3506-1)
  • Flange Types: Plain (non-serrated) and Serrated — both available in the same size range
  • Integrated Flange: Eliminates need for a separate flat washer — reduces parts count and assembly time
  • Serrated Flange Anti-Loosening: Knurled underside bites into mating surface, resisting vibration-induced loosening without adhesives
  • Drive: External hex (spanner / wrench), full hex head
  • Thread: Metric coarse thread (ISO 68-1), right-hand
  • Surface: Natural (as-machined) stainless — no coating required
  • Size Range: M5 to M20

Plain Flange vs. Serrated Flange: Choosing the Right Type

Feature Plain (Non-Serrated) Flange Serrated Flange
Flange Underside Smooth, flat Knurled / serrated teeth
Anti-Loosening Standard — friction only ✅ Mechanical — teeth bite into mating surface
Vibration Resistance Standard ✅ Enhanced — preferred for dynamic loads
Surface Marking ✅ No marking — suitable for finished surfaces ⚠️ Leaves serration marks on mating surface
Reusability ✅ Full reusability — no surface damage ⚠️ Reduced — serrations wear with repeated removal
Torque Transmission Standard friction-based Higher effective clamp due to serration engagement
Best For General assemblies, finished/coated surfaces, frequent disassembly Vibration-prone assemblies, automotive, machinery, structural joints
DIN Reference DIN 6921 (plain) DIN 6921 with serration (DIN 6923 equivalent geometry)

Material & Mechanical Properties

Manufactured from A2 stainless steel (SUS304 / EN 1.4301) — the most widely used austenitic stainless steel, offering an excellent balance of corrosion resistance, formability, and weldability.

Property Value Standard Reference
Material Grade A2 (SUS304 / 1.4301) ISO 3506 / EN 10088
Property Class A2-70 ISO 3506-1
Tensile Strength (min.) 700 MPa ISO 3506-1
0.2% Proof Stress (min.) 450 MPa ISO 3506-1
Elongation (min.) 20% ISO 3506-1
Hardness (max.) 220 HV ISO 3506-1
Chromium Content 17.5 – 19.5% EN 10088
Nickel Content 8.0 – 10.5% EN 10088
Magnetic Non-magnetic (annealed state) —
Corrosion Resistance Excellent — atmospheric, freshwater, mild chemical —
Operating Temperature −50°C to +300°C (continuous) —

Dimensional Specifications (DIN 6921)

All dimensions per DIN 6921. Thread per ISO 68-1 metric coarse. Flange diameter (dc) and flange thickness (c) are the same for both plain and serrated variants.

Size Thread Pitch (mm) Wrench Size s (mm) Head Height k (mm) Flange Dia. dc (mm) Flange Thickness c (mm) Common Lengths (mm)
M5 0.8 8 3.65 11.8 1.0 10, 12, 16, 20, 25, 30, 35, 40
M6 1.0 10 4.15 14.2 1.1 10, 12, 16, 20, 25, 30, 35, 40, 50
M8 1.25 13 5.45 17.9 1.2 12, 16, 20, 25, 30, 35, 40, 50, 60
M10 1.5 15 6.58 21.8 1.5 16, 20, 25, 30, 35, 40, 50, 60, 70, 80
M12 1.75 18 7.68 26.0 1.8 20, 25, 30, 35, 40, 50, 60, 70, 80, 100
M14 2.0 21 8.98 29.9 2.1 25, 30, 35, 40, 50, 60, 70, 80, 100
M16 2.0 24 10.18 34.5 2.4 25, 30, 35, 40, 50, 60, 70, 80, 100, 120
M20 2.5 30 12.72 42.8 3.0 30, 35, 40, 50, 60, 70, 80, 100, 120

All dimensions are nominal per DIN 6921. Consult FULLERKREG product listings for exact available size/length combinations. Tolerances per ISO 4759-1. Thread length per DIN 6921 / ISO 4016 grip length rules.

How the Integrated Flange Works

The DIN 6921 flange serves as a permanently attached, load-spreading washer:

  • Larger bearing area: The flange diameter (dc) is significantly larger than the hex head across-flats dimension (s), distributing the clamping force over a wider surface area and reducing surface pressure on the clamped material.
  • No separate washer needed: Eliminates washer procurement, handling, and the risk of washer loss or misalignment during assembly.
  • Consistent clamp load: The flange geometry is fixed and repeatable — no variation from washer placement or stacking.
  • Serrated variant: The knurled underside of the serrated flange engages the mating surface as the bolt is tightened, creating a mechanical interlock that resists rotational loosening under vibration and dynamic loads — without thread-locking adhesives.

Corrosion Resistance of A2 Stainless Steel

A2 (SUS304) stainless steel forms a self-repairing passive chromium oxide layer, providing durable corrosion protection across a wide range of environments:

  • ✅ Atmospheric exposure — urban, industrial, and rural environments
  • ✅ Freshwater immersion — potable water systems, food processing
  • ✅ Mild chemical exposure — dilute acids, alkalis, and organic compounds
  • ✅ Food contact — non-toxic, non-leaching; compliant with food-grade requirements
  • ⚠️ Chloride environments — susceptible to pitting in high-chloride (marine/coastal) conditions; use A4 (SUS316) for such applications
  • ❌ Strong reducing acids (e.g., hydrochloric, sulphuric) — not recommended

Typical Applications

  • Plain Flange: General mechanical assemblies, food processing equipment, architectural metalwork, electrical enclosures, and any application where surface marking must be avoided
  • Serrated Flange: Automotive body panels and chassis, HVAC ductwork, machinery frames, conveyor systems, sheet metal assemblies, and any vibration-prone joint where a separate lock washer would otherwise be required
  • Thin-sheet metal fastening where a standard hex bolt would pull through without a washer
  • Marine deck hardware and boat fittings in sheltered/freshwater environments
  • Pharmaceutical and cleanroom equipment requiring corrosion-free, non-magnetic fasteners
  • Structural brackets, flanged pipe connections, and equipment mounting in corrosive environments

Installation & Torque Guidelines

Recommended installation torque values for A2-70 DIN 6921 flanged hex bolts (dry, unlubricated, μ = 0.12). Note: the flange increases the effective bearing area, which slightly reduces the required torque compared to a standard hex bolt of the same size with a separate washer.

Size Recommended Torque — Plain Flange (N·m) Recommended Torque — Serrated Flange (N·m) Wrench Size (mm)
M5 3.5 – 4.5 3.0 – 4.0 8
M6 6.0 – 7.5 5.5 – 7.0 10
M8 14 – 17 13 – 16 13
M10 28 – 34 26 – 32 15
M12 48 – 58 45 – 55 18
M14 77 – 92 72 – 87 21
M16 120 – 144 112 – 135 24
M20 235 – 280 220 – 265 30

Torque values are indicative for dry conditions (μ = 0.12). Lubrication reduces required torque by approximately 20–25%. For critical joints, use a calibrated torque wrench. A2 stainless is susceptible to galling — apply anti-seize compound (molybdenum disulphide or PTFE-based) for M10 and above, or where repeated assembly/disassembly is required.

Anti-Galling Note for Stainless Steel Fasteners

Stainless steel fasteners — including A2 — are prone to galling (cold welding / thread seizure) during installation. To prevent galling:

  • Apply a thin coat of anti-seize compound (molybdenum disulphide, copper-based, or PTFE-based) to the thread and under the flange before installation
  • Drive at low speed — avoid high-speed power tools without torque control
  • Ensure threads are clean and free of debris before assembly
  • Use A2 nuts with A2 bolts — mixing grades increases galling risk
  • If galling occurs during removal, apply penetrating oil and use a slow, steady torque — do not force

Compliance & Standards

  • DIN 6921 — Hexagon bolts with flange (metric)
  • ISO 3506-1 — Mechanical properties of corrosion-resistant stainless steel fasteners — bolts, screws and studs
  • DIN 267-11 — Fasteners: Technical specifications — property classes for stainless steel
  • ISO 68-1 — Metric screw threads: General plan
  • ISO 4759-1 — Tolerances for fasteners
  • EN 10088 — Stainless steels: List of stainless steels (1.4301 / SUS304)
  • RoHS compliant — no restricted substances in A2 stainless steel

Packaging & Supply

  • Available in bulk bags, plastic boxes, and custom packaging for OEM and MRO supply
  • Both plain flange and serrated flange types stocked in standard sizes
  • Standard packaging quantities: 10 pcs, 25 pcs, 50 pcs, 100 pcs, 500 pcs (size-dependent)
  • Wholesale and B2B pricing available — contact FULLERKREG for volume quotations
  • Full material certifications (mill certs, ISO 3506 compliance) available on request
  • Custom lengths and non-standard sizes available on request (MOQ applies)
  • RoHS and REACH compliant documentation available

Why Choose FULLERKREG DIN 6921 A2 Flanged Hex Bolts?

  • Integrated flange eliminates separate washer — reduces parts count, assembly time, and risk of washer loss
  • Both plain and serrated flange types available — one product family covers standard and vibration-resistant applications
  • A2 (SUS304) stainless steel — excellent corrosion resistance for food, architectural, and industrial use
  • A2-70 mechanical properties verified per ISO 3506-1 with full material traceability
  • Manufactured to DIN 6921 dimensional standards — not nominal equivalents
  • Full size range M5–M20 with broad length availability for versatile application coverage
  • Competitive lead times for standard sizes; custom configurations on request
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