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DIN 603 Carriage Bolt 4.8 Hot Dip Galvanized

DIN 603 Carriage Bolt — Grade 4.8 | Hot Dip Galvanized | FULLERKREG

FULLERKREG DIN 603 Hot Dip Galvanized Carriage Bolts are engineered for demanding outdoor, structural, and heavy-duty applications where long-term corrosion resistance is critical. The hot dip galvanizing process deposits a thick, metallurgically bonded zinc coating that provides far superior protection compared to electroplated alternatives — making these bolts the preferred choice for timber construction, civil infrastructure, agricultural structures, and any application exposed to moisture, weather, or corrosive environments.

Product Overview

  • Standard: DIN 603
  • Common Name: Carriage Bolt / Coach Bolt / Round Head Square Neck Bolt
  • Material: Low Carbon Steel Q195
  • Property Class / Grade: 4.8 (per DIN EN ISO 898-1)
  • Surface Treatment: Hot Dip Galvanized (HDG)
  • Thread: Metric coarse thread (ISO 68-1)
  • Head Type: Round (domed) head with square neck
  • Brand: FULLERKREG

What Is a DIN 603 Carriage Bolt?

The DIN 603 carriage bolt — also known as a coach bolt or round head square neck bolt — is a specialized fastener defined by three key geometric features that make it uniquely suited to timber and structural applications:

  • Smooth Domed Head: The low-profile, rounded head presents a clean, tamper-resistant appearance on the visible face of the joint. No drive recess is present — the bolt is tightened exclusively from the nut side, providing a smooth, snag-free surface.
  • Square Neck (Collar): Immediately below the head, a short square section embeds into the timber substrate or a pre-punched square hole when the nut is tightened, preventing the bolt from rotating. This enables single-sided tightening with a wrench on the nut alone — no tool required on the bolt head side.
  • Threaded Shank: The shank carries a metric coarse thread accepting a standard hex nut or flange nut. Shorter lengths may be fully threaded; longer lengths feature an unthreaded grip section.

Material: Low Carbon Steel Q195

Q195 is a Chinese national standard (GB/T 700) low carbon structural steel with excellent cold-forming characteristics, making it the ideal base material for high-volume carriage bolt production. Its low carbon content ensures outstanding ductility and weldability, while providing sufficient strength for Grade 4.8 mechanical requirements.

  • Carbon Content: ≤ 0.12% C (ultra-low carbon, excellent formability)
  • Manganese: 0.25 – 0.50% Mn
  • Yield Strength: ≥ 195 MPa
  • Tensile Strength: 315 – 430 MPa
  • Elongation: ≥ 33%
  • Weldability: Excellent — suitable for welded structural assemblies
  • Cold-Heading: Excellent — ideal for high-volume bolt production
  • HDG Compatibility: Low carbon content minimizes risk of hydrogen embrittlement and ensures excellent zinc adhesion during galvanizing

Mechanical Properties — Grade 4.8

Property Specification Standard Reference
Material Low Carbon Steel Q195 DIN EN ISO 898-1
Property Class 4.8 DIN EN ISO 898-1
Nominal Tensile Strength (Rm) ≥ 420 MPa DIN EN ISO 898-1
Proof Load Stress (Sp) 310 MPa DIN EN ISO 898-1
Yield Strength (Rp0.2) ≥ 340 MPa (80% of Rm) DIN EN ISO 898-1
Hardness (Vickers) 130 – 220 HV DIN EN ISO 898-1
Elongation after fracture ≥ 14% DIN EN ISO 898-1
Surface Treatment Hot Dip Galvanized (HDG) ISO 1461 / EN ISO 10684
Zinc Coating Thickness ≥ 45 µm (typical 50 – 85 µm) ISO 1461
Corrosion Resistance (NSS) ≥ 1,000 hours neutral salt spray ISO 9227

Hot Dip Galvanizing: Process & Performance

Hot dip galvanizing (HDG) is the most robust zinc coating process available for carbon steel fasteners. Unlike electroplating, which deposits a thin zinc layer through electrical current, HDG immerses the cleaned steel in a bath of molten zinc at approximately 450°C, forming a series of zinc-iron alloy layers topped by a pure zinc outer layer. The result is a coating that is metallurgically bonded to the steel — not merely adhered — providing exceptional durability and self-healing properties.

HDG Process Steps

  1. Degreasing: Removal of oils, grease, and organic contaminants
  2. Pickling: Acid cleaning to remove mill scale and rust
  3. Fluxing: Application of zinc ammonium chloride flux to prevent oxidation before galvanizing
  4. Galvanizing: Immersion in molten zinc bath at ~450°C for controlled dwell time
  5. Quenching & Inspection: Cooling, visual inspection, and coating thickness verification per ISO 1461

HDG Coating Structure

  • Gamma layer (Γ): ~5 µm — zinc-iron alloy (innermost, highest iron content)
  • Delta layer (δ): ~20 µm — zinc-iron alloy (intermediate)
  • Zeta layer (ζ): ~15 µm — zinc-iron alloy (columnar crystals)
  • Eta layer (η): ~10–20 µm — pure zinc (outermost, provides cathodic protection)

Key Performance Advantages vs. Electroplating

Property Hot Dip Galvanized (HDG) Zinc Electroplate (CR3)
Coating Thickness 45 – 85 µm 5 – 12 µm
Bond Type Metallurgical (alloy bond) Mechanical adhesion
Salt Spray Resistance ≥ 1,000 hours 24 – 48 hours (Grade 4.8)
Outdoor Service Life 20 – 50+ years (rural/urban) 2 – 5 years (exposed)
Cathodic Protection Yes — sacrificial zinc protects exposed steel Limited
Self-Healing Yes — zinc oxide/carbonate forms at scratches No
Appearance Matte grey / spangled Bright silver / blue-clear
Thread Fit Requires oversize tapping (coating adds bulk) Standard thread fit
Best For Outdoor, structural, heavy-duty Indoor, light-duty, precision fit

Dimensional Reference — DIN 603 Key Parameters

Note: Hot dip galvanizing adds 45–85 µm of coating per surface. Nuts must be tapped oversize (typically one tolerance class) to accommodate the coating thickness on threaded sections.

Thread Size Pitch (mm) Head Diameter dk (mm) Head Height k (mm) Square Neck Width f (mm) Square Neck Height m (mm)
M5 0.8 14.0 3.0 5.0 3.5
M6 1.0 16.0 3.6 6.0 4.0
M8 1.25 21.0 4.8 8.0 5.0
M10 1.5 26.0 6.0 10.0 6.0
M12 1.75 30.0 7.2 12.0 7.0
M14 2.0 35.0 8.4 14.0 8.0
M16 2.0 40.0 9.6 16.0 9.0
M20 2.5 50.0 12.0 20.0 11.0

Standard lengths range from 16 mm to 300 mm depending on thread size. Full dimensional tables per DIN 603. Custom lengths available upon request.

Typical Application Sectors

🏗️ Structural Timber & Heavy Construction

  • Timber frame and post-and-beam structural connections
  • Glulam beam and engineered timber (LVL, CLT) assembly
  • Bridge decking and boardwalk timber fastening
  • Retaining wall timber crib and sleeper connections
  • Formwork and falsework structural joints
  • Scaffold and temporary works connections

🌳 Outdoor & Landscape Structures

  • Decking, pergola, gazebo, and garden structure assembly
  • Fence post, rail, and gate hardware fastening
  • Outdoor furniture — park benches, picnic tables, and seating
  • Playground equipment — climbing frames, swing sets, and slides
  • Jetty, pontoon, and marine timber structure fastening
  • Outdoor signage and display structure mounting

🌾 Agricultural & Rural Infrastructure

  • Farm building and barn structural connections
  • Livestock pen, stable, and yard fencing
  • Grain store and silo structural fastening
  • Agricultural machinery guards and covers
  • Irrigation system support structures

⚡ Civil & Infrastructure Projects

  • Railway sleeper and track infrastructure fastening
  • Utility pole and transmission tower base connections
  • Coastal and marine infrastructure — piers, jetties, and sea walls
  • Highway noise barrier and crash barrier structural joints
  • Water treatment and wastewater facility structural fastening

Key Features & Design Advantages

  • 🛡️ Maximum Corrosion Protection: HDG zinc coating of 45–85 µm provides decades of outdoor service life — far exceeding electroplated alternatives. Ideal for permanently exposed structural joints.
  • 🔒 Anti-Rotation Square Neck: The square collar embeds into timber or a pre-punched square hole, preventing bolt rotation during nut tightening — enabling single-sided assembly.
  • ❤️ Cathodic (Sacrificial) Protection: Even if the zinc coating is scratched or damaged, the surrounding zinc acts as a sacrificial anode, protecting the exposed steel from rusting — a unique self-healing property not available with paint or electroplate.
  • 📏 Tamper-Resistant Smooth Head: The domed head has no drive recess, providing a clean appearance and resistance to unauthorized removal without nut-side access.
  • ⚙️ Metallurgical Bond: Unlike adhesive coatings, the HDG zinc-iron alloy layers are bonded at the atomic level — the coating cannot peel, flake, or delaminate under mechanical stress.
  • ✅ Long Service Life: In rural atmospheric conditions, HDG fasteners typically provide 50+ years of maintenance-free service. In urban or industrial environments, 20–30 years is typical.

Installation Notes for HDG Carriage Bolts

  1. Nut Selection: Always use HDG nuts (tapped oversize) with HDG bolts. Standard-tolerance nuts will not fit due to the additional coating thickness on the thread. Specify HDG nuts when ordering.
  2. Hole Preparation: Drill clearance holes to the nominal bolt diameter. The HDG coating adds minimal bulk to the shank — standard clearance holes are generally acceptable.
  3. Square Neck Embedding: Insert the bolt from the front face and tap lightly with a mallet to seat the square neck into the timber. The HDG coating on the square neck provides additional grip in the timber substrate.
  4. Washer Recommendation: Use HDG flat washers under the nut to prevent pull-through in timber and to protect the timber surface from the nut bearing face.
  5. Tightening: Tighten from the nut side only. Do not use impact tools at excessive torque — the HDG coating on the thread may be damaged by overtightening.
  6. Galvanic Compatibility: When fastening aluminium or copper components, use isolation washers or sleeves to prevent galvanic corrosion between dissimilar metals.

Recommended Tightening Torque — Grade 4.8

Thread Size Tightening Torque (Nm) — Dry Tightening Torque (Nm) — Lubricated
M5 2.5 1.9
M6 4.3 3.2
M8 10.5 7.9
M10 21 16
M12 36 27
M14 57 43
M16 88 66
M20 172 129

Torque values are indicative for Grade 4.8 bolts at 70% proof load. Always verify with your structural engineer for safety-critical applications.

Why Choose FULLERKREG HDG DIN 603 Carriage Bolts?

  • ✅ Full DIN 603 & ISO 1461 Compliance: Every batch manufactured to DIN 603 dimensional standards, Grade 4.8 mechanical requirements, and ISO 1461 hot dip galvanizing specifications.
  • ✅ Thick, Durable HDG Coating: Minimum 45 µm zinc coating — providing decades of outdoor corrosion protection far beyond electroplated alternatives.
  • ✅ Full Traceability: Material certificates (MTC), mechanical test reports, coating thickness inspection records, and salt spray test data available per shipment.
  • ✅ High-Volume Production Capability: Consistent lot-to-lot quality for construction, civil engineering, and infrastructure procurement programs.
  • ✅ Wide Size Range: M5 through M20, lengths from 16 mm to 300 mm — covering the full DIN 603 range.
  • ✅ Matched HDG Nuts & Washers Available: Complete HDG fastener sets (bolt + nut + washer) available for simplified procurement.
  • ✅ Flexible Packaging: Bulk, box, and pallet options available to suit construction site and project requirements.

Applicable Standards & References

  • DIN 603 — Round head square neck bolts (metric coarse thread)
  • DIN EN ISO 898-1 — Mechanical properties of fasteners: bolts, screws and studs (property class 4.8)
  • ISO 1461 — Hot dip galvanized coatings on fabricated iron and steel articles — specifications and test methods
  • EN ISO 10684 — Fasteners — hot dip galvanized coatings
  • ISO 9227 — Corrosion tests in artificial atmospheres — neutral salt spray (NSS) test
  • GB/T 700 — Carbon structural steels (Q195 material standard)
  • ISO 4014 / ISO 4016 — Hexagon head bolts (referenced for thread and shank geometry)

Ordering & Customization

FULLERKREG supplies DIN 603 Grade 4.8 Hot Dip Galvanized carriage bolts in standard and custom configurations. Please specify the following when placing an inquiry:

  • Thread diameter and pitch (e.g., M8 × 1.25, M12 × 1.75)
  • Nominal length (e.g., 40 mm, 80 mm, 150 mm)
  • Fully threaded or partially threaded shank preference
  • Whether matched HDG nuts and washers are required
  • Required quantity and packaging format (bulk / box / pallet)
  • Certification requirements (ISO 1461 coating reports, material certificates, mechanical test reports)

Contact our technical sales team for datasheets, samples, and volume pricing.

FULLERKREG — Reliable Fasteners Built to Last. Hot Dip Galvanized for Decades of Outdoor Performance.

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