Home » DIN 603 Carriage Bolt 4.8 Zinc CR3

DIN 603 Carriage Bolt 4.8 Zinc CR3

DIN 603 Carriage Bolt — Grade 4.8 | Zinc CR3 | FULLERKREG

FULLERKREG DIN 603 Carriage Bolts are precision-manufactured round-head square-neck bolts designed for wood-to-wood, wood-to-metal, and general structural fastening applications. Produced to the full dimensional requirements of DIN 603, these bolts feature a smooth domed head, a square neck that locks into the substrate to prevent rotation during tightening, and a fully threaded or partially threaded shank depending on length. The Zinc CR3 (trivalent chromate) surface finish provides reliable corrosion protection while meeting RoHS and ELV environmental compliance requirements.

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: Zinc CR3 (trivalent chromate zinc electroplate)
  • 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 distinguished by three key geometric features:

  • 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 on the head — the bolt is tightened exclusively from the nut side.
  • Square Neck (Collar): Immediately below the head, a short square section embeds into the substrate (typically timber or a pre-punched square hole in sheet metal) when the nut is tightened, preventing the bolt from rotating. This allows single-sided tightening with a wrench on the nut alone.
  • Threaded Shank: The remainder of the shank is threaded (metric coarse), accepting a standard hex nut or flange nut. Shorter lengths may be fully threaded; longer lengths have an unthreaded shank section.

Material: Low Carbon Steel Q195

Q195 is a Chinese national standard (GB/T 700) low carbon structural steel, equivalent in composition and mechanical behavior to S185 (EN 10025) and ASTM A36 in the low-strength range. It is the standard material for Grade 4.8 fasteners requiring good ductility, easy cold-forming, and reliable weldability.

  • 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 assemblies
  • Cold-Heading: Excellent — ideal for high-volume bolt production
  • Magnetic: Yes (ferritic steel)

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 Zinc CR3 (trivalent chromate electroplate) DIN 267-11
Corrosion Resistance 24 – 48 hours neutral salt spray (NSS) DIN 267-11 / ISO 9227

Dimensional Reference — DIN 603 Key Parameters

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.

Surface Treatment: Zinc CR3 (Trivalent Chromate)

All FULLERKREG DIN 603 carriage bolts are finished with a Zinc CR3 electroplated coating — the automotive and construction industry standard for RoHS-compliant corrosion protection on carbon steel fasteners.

  • Chromate Type: Trivalent chromate (Cr³⁺) — zero hexavalent chromium (Cr⁶⁺)
  • Appearance: Bright silver / clear to light blue iridescent finish
  • Corrosion Protection: 24 – 48 hours neutral salt spray (NSS) to first red rust (per ISO 9227)
  • Coating Standard: DIN 267-11 / DIN EN ISO 4042
  • Coating Thickness: Typically 5 – 12 µm
  • RoHS Compliant: ✅ Yes — no restricted hazardous substances
  • ELV Directive Compliant: ✅ Yes — suitable for automotive and construction supply chains requiring environmental compliance
  • REACH Compliant: ✅ Yes

Key Features & Design Advantages

  • 🔒 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 with no tool access required on the bolt head side.
  • 🛡️ Tamper-Resistant Smooth Head: The domed head has no drive recess, making it difficult to remove without access to the nut — ideal for public-facing or security-sensitive installations.
  • 📏 Clean Aesthetic: The smooth, low-profile round head provides a neat, professional appearance on the visible face of the joint — preferred in furniture, playground equipment, and architectural woodwork.
  • ⚙️ Versatile Substrate Compatibility: Designed primarily for timber, but also used with pre-punched square holes in steel plate, aluminium extrusions, and composite panels.
  • ✅ Single-Sided Tightening: Ideal for applications where only one face of the joint is accessible during assembly.

Typical Application Sectors

🏗️ Construction & Structural Timber

  • Timber frame connections — beams, joists, rafters, and purlins
  • Decking and outdoor timber platform assembly
  • Fence post and rail connections
  • Pergola, gazebo, and garden structure fastening
  • Staircase stringers and handrail brackets
  • Formwork and temporary structural connections

🪑 Furniture & Joinery

  • Flat-pack and knock-down (KD) furniture assembly
  • Bed frames, table bases, and bench seating
  • Cabinet and shelving unit structural joints
  • Upholstered furniture frame fastening

🎪 Playground & Outdoor Equipment

  • Playground equipment — climbing frames, slides, and swing sets
  • Park benches and outdoor seating
  • Sports facility structures and bleacher seating
  • Outdoor signage and display structures

🚚 Agricultural & Industrial Equipment

  • Agricultural machinery guards and covers
  • Conveyor frame and material handling equipment
  • Storage rack and shelving systems
  • General industrial structural assembly

Installation Guide

  1. Prepare the substrate: Drill a clearance hole equal to the bolt diameter through both members to be joined. For timber, the square neck will self-embed; for metal, punch or drill a square hole matching the neck dimensions.
  2. Insert the bolt: Push the carriage bolt through the hole from the front (visible) face. The domed head sits flush against the surface.
  3. Embed the square neck: Tap the bolt head lightly with a mallet if needed to seat the square neck fully into the timber or square hole, preventing rotation.
  4. Apply washer and nut: Place a flat washer (recommended for timber to prevent pull-through) and hex nut on the threaded end.
  5. Tighten from the nut side: Use a wrench or socket on the nut only. The embedded square neck prevents the bolt from turning. Tighten to the recommended torque for Grade 4.8 and the thread size.

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 DIN 603 Carriage Bolts?

  • ✅ Consistent DIN 603 Compliance: Every batch manufactured and inspected to DIN 603 dimensional standards and DIN EN ISO 898-1 mechanical requirements.
  • ✅ RoHS & ELV Compliant Zinc CR3 Finish: Trivalent chromate coating — no hexavalent chromium — meets EU environmental directives for global supply chains.
  • ✅ Full Traceability: Material certificates (MTC), mechanical test reports, and salt spray test records available per shipment.
  • ✅ High-Volume Production Capability: Consistent lot-to-lot quality for construction, furniture, and industrial procurement programs.
  • ✅ Wide Size Range: M5 through M20, lengths from 16 mm to 300 mm — covering the full DIN 603 range.
  • ✅ Flexible Packaging: Bulk, box, and custom packaging options available to suit project and assembly line requirements.
  • ✅ Competitive Lead Times: Direct factory supply with efficient global logistics.

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)
  • DIN 267-11 — Fasteners: technical delivery conditions — electroplated coatings
  • DIN EN ISO 4042 — Fasteners: electroplated coatings
  • ISO 9227 — Corrosion tests in artificial atmospheres — neutral salt spray (NSS) test
  • GB/T 700 — Carbon structural steels (Q195 material standard)
  • RoHS Directive 2011/65/EU — Restriction of hazardous substances
  • ELV Directive 2000/53/EC — End-of-life vehicles (hexavalent chromium restriction)

Ordering & Customization

FULLERKREG supplies DIN 603 Grade 4.8 Zinc CR3 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., 30 mm, 60 mm, 100 mm)
  • Fully threaded or partially threaded shank preference
  • Required quantity and packaging format (bulk / box / pallet)
  • Certification requirements (material certificates, salt spray test reports, dimensional inspection reports)

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

FULLERKREG — Reliable Fasteners for Construction, Industry, and Beyond.

Sorry, this collection is empty.
Continue shopping