Home » DIN 603 Carriage Bolt 8.8 Zinc CR3

DIN 603 Carriage Bolt 8.8 Zinc CR3

DIN 603 Carriage Bolt — Grade 8.8 | Zinc CR3 | FULLERKREG

FULLERKREG DIN 603 Grade 8.8 Zinc CR3 Carriage Bolts are high-strength round-head square-neck bolts engineered for structural and load-bearing applications that demand greater clamping force than standard Grade 4.8 fasteners. Manufactured from Alloy Steel 10B21 (boron steel) or Carbon Steel 35K and finished with a RoHS-compliant Zinc CR3 (trivalent chromate) electroplated coating, these bolts combine the anti-rotation convenience of the classic DIN 603 carriage bolt design with the mechanical performance required for demanding structural, industrial, and heavy-duty assembly applications.

Product Overview

  • Standard: DIN 603
  • Common Name: High-Strength Carriage Bolt / Coach Bolt / Round Head Square Neck Bolt
  • Material: Alloy Steel 10B21 (boron steel) or Carbon Steel 35K
  • Property Class / Grade: 8.8 (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 defined by three key geometric features that make it uniquely suited to applications requiring single-sided assembly:

  • 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, leaving a smooth, snag-free surface.
  • Square Neck (Collar): Immediately below the head, a short square section embeds into the substrate (timber or a pre-punched square hole in metal) when the nut is tightened, preventing the bolt from rotating. This enables single-sided tightening with a wrench on the nut alone — no tool access 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.

Grade 8.8 vs Grade 4.8: The Grade 8.8 variant delivers approximately double the tensile strength of the standard Grade 4.8 carriage bolt, making it the preferred choice for structural timber connections, heavy machinery, and load-bearing joints where higher clamping forces are required.

Material Options

Option A — Alloy Steel 10B21 (Boron Steel)

10B21 is a boron-alloyed low-carbon steel that is the preferred material for high-volume automotive and structural fastener production. The addition of boron (typically 0.0005–0.003%) dramatically improves hardenability, allowing Grade 8.8 mechanical properties to be achieved with lower alloy content and excellent cold-forging characteristics.

  • Carbon Content: ~0.18–0.23% C
  • Boron Addition: 0.0005–0.003% B — significantly improves hardenability
  • Superior hardenability vs plain carbon steel — consistent mechanical properties across large cross-sections
  • Excellent cold-heading formability — ideal for high-volume production with tight dimensional tolerances
  • Preferred material for automotive OEM and Tier-1 structural fastener supply chains
  • Consistent mechanical properties across large production lots

Option B — Carbon Steel 35K

35K is a medium-carbon steel offering a reliable balance of strength and toughness at an economical cost. Suitable for Grade 8.8 fasteners in general structural and industrial applications where boron-alloyed steel is not specifically required.

  • Carbon Content: ~0.32–0.39% C (medium carbon)
  • Good balance of tensile strength and ductility for Grade 8.8 requirements
  • Cost-effective for high-volume standard structural fastener applications
  • Widely available and well-understood in global supply chains
  • Suitable for non-critical structural joints and general heavy-duty assembly

Mechanical Properties — Grade 8.8

Property Specification Standard Reference
Material Alloy Steel 10B21 or Carbon Steel 35K DIN EN ISO 898-1
Property Class 8.8 DIN EN ISO 898-1
Nominal Tensile Strength (Rm) ≥ 800 MPa DIN EN ISO 898-1
Proof Load Stress (Sp) 600 MPa DIN EN ISO 898-1
Yield Strength (Rp0.2) ≥ 640 MPa DIN EN ISO 898-1
Hardness (Vickers) 250 – 320 HV DIN EN ISO 898-1
Core Hardness (Rockwell) 22 – 32 HRC DIN EN ISO 898-1
Elongation after fracture ≥ 12% DIN EN ISO 898-1
Surface Treatment Zinc CR3 (trivalent chromate electroplate) DIN 267-11
Corrosion Resistance (NSS) 72 – 120 hours neutral salt spray DIN 267-11 / ISO 9227
Coating Thickness Typically 5 – 12 µm DIN EN ISO 4042

Grade Comparison: 4.8 vs 8.8

Property Grade 4.8 (Standard) Grade 8.8 (This Product) Improvement
Tensile Strength (Rm) ≥ 420 MPa ≥ 800 MPa +90%
Yield Strength (Rp0.2) ≥ 340 MPa ≥ 640 MPa +88%
Proof Load Stress (Sp) 310 MPa 600 MPa +94%
Hardness 130 – 220 HV 250 – 320 HV Higher
Material Low Carbon Steel Q195 Alloy Steel 10B21 / Carbon Steel 35K Higher alloy
Typical Use Light structural, timber, furniture Heavy structural, machinery, load-bearing —

Surface Treatment: Zinc CR3 (Trivalent Chromate)

FULLERKREG DIN 603 Grade 8.8 carriage bolts are finished with a Zinc CR3 electroplated coating — the industry standard for RoHS-compliant corrosion protection on high-strength carbon and alloy steel fasteners.

  • Chromate Type: Trivalent chromate (Cr³⁺) — zero hexavalent chromium (Cr⁶⁺)
  • Appearance: Bright silver / clear to light blue iridescent finish
  • Corrosion Protection: 72 – 120 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 industrial supply chains
  • REACH Compliant: ✅ Yes
  • Hydrogen Embrittlement Relief: Controlled baking process post-plating per DIN EN ISO 4042 — critical for Grade 8.8 high-strength fasteners to eliminate embrittlement risk

⚠️ Important — Hydrogen Embrittlement: Grade 8.8 fasteners with hardness ≥ 320 HV are susceptible to hydrogen embrittlement during electroplating. FULLERKREG applies a controlled post-plating baking process (typically 200°C for ≥ 4 hours) per DIN EN ISO 4042 to eliminate absorbed hydrogen and ensure the mechanical integrity of every Grade 8.8 bolt.

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 20 mm to 300 mm depending on thread size. Full dimensional tables per DIN 603. Custom lengths available upon request.

Typical Application Sectors

🏗️ Heavy Structural Timber & Construction

  • Heavy timber frame and post-and-beam structural connections requiring high clamping force
  • Glulam beam, LVL, and engineered timber (CLT) structural joints
  • Timber bridge decking and heavy boardwalk structural fastening
  • Retaining wall timber crib connections under high lateral load
  • Scaffold and falsework structural joints requiring certified load capacity
  • Prefabricated timber building module connections

⚙️ Industrial Machinery & Equipment

  • Heavy machinery base plate and frame fastening
  • Conveyor system structural connections and drive unit mounting
  • Material handling equipment — crane, hoist, and lifting frame fastening
  • Compressor, pump, and motor base fastening
  • Industrial press and stamping machine structural connections
  • Mining and quarrying equipment structural fastening

🚚 Transportation & Vehicle Structures

  • Truck body and trailer structural connections
  • Bus and coach body frame fastening
  • Railway wagon and rolling stock structural joints
  • Agricultural machinery and implement structural fastening
  • Construction vehicle cab and body structural connections

🌳 Outdoor & Infrastructure Structures

  • Heavy-duty playground and recreational equipment structural fastening
  • Sports facility bleacher and grandstand structural connections
  • Highway noise barrier and crash barrier structural joints
  • Utility pole and transmission tower base connections
  • Solar panel mounting structure heavy-duty connections

Key Features & Design Advantages

  • 💪 High-Strength Grade 8.8: Tensile strength ≥ 800 MPa — approximately double the strength of standard Grade 4.8 carriage bolts. Suitable for load-bearing structural joints where higher clamping forces are required.
  • 🔒 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.
  • ✅ Dual Material Options: Choose between Alloy Steel 10B21 (boron steel, preferred for OEM and high-volume structural supply) or Carbon Steel 35K (cost-effective for general structural applications) — both meeting Grade 8.8 mechanical requirements.
  • 🛡️ RoHS-Compliant Zinc CR3 Finish: Trivalent chromate coating — no hexavalent chromium — meets EU environmental directives for global supply chains.
  • ⚠️ Hydrogen Embrittlement Controlled: Post-plating baking process per DIN EN ISO 4042 eliminates hydrogen embrittlement risk — critical for Grade 8.8 high-strength fasteners.
  • 📏 Tamper-Resistant Smooth Head: The domed head has no drive recess, providing a clean appearance and resistance to unauthorized removal without nut-side access.
  • 📊 Full Traceability: Material certificates, mechanical test reports, hardness test records, and coating inspection data available per shipment.

Installation Guide

  1. Verify substrate compatibility: Grade 8.8 carriage bolts generate significantly higher clamping forces than Grade 4.8. Ensure the substrate (timber species, metal thickness, or composite material) is rated for the increased bearing stress at the bolt head and nut contact areas.
  2. Prepare the substrate: Drill a clearance hole equal to the bolt diameter. For timber, the square neck will self-embed; for metal, punch or drill a square hole matching the neck dimensions.
  3. Insert the bolt: Push the carriage bolt through the hole from the front (visible) face.
  4. Embed the square neck: Tap the bolt head firmly with a mallet to seat the square neck fully into the timber or square hole. Grade 8.8 bolts require firm seating to prevent rotation under higher tightening torques.
  5. Apply washer and nut: Place a hardened flat washer (Grade 8 or equivalent) and Grade 8 hex nut on the threaded end. Use a washer under the nut to distribute the higher clamping load and prevent pull-through or surface damage.
  6. Tighten from the nut side: Use a calibrated torque wrench to tighten to the recommended torque for Grade 8.8 and the thread size. Do not exceed the maximum torque — Grade 8.8 fasteners are susceptible to torsional fracture if overtightened.

Recommended Tightening Torque — Grade 8.8

Thread Size Tightening Torque (Nm) — Dry Tightening Torque (Nm) — Lubricated
M5 6.0 4.5
M6 10.4 7.8
M8 25 19
M10 50 38
M12 87 65
M14 138 104
M16 213 160
M20 415 311

Torque values are indicative for Grade 8.8 bolts at 70% proof load. Use a calibrated torque wrench for structural applications. Always verify with your structural engineer for safety-critical joints.

Why Choose FULLERKREG DIN 603 Grade 8.8 Zinc CR3?

  • ✅ Full DIN 603 & ISO 898-1 Compliance: Every batch manufactured to DIN 603 dimensional standards and DIN EN ISO 898-1 Grade 8.8 mechanical requirements.
  • ✅ Hydrogen Embrittlement Controlled: Post-plating baking process per DIN EN ISO 4042 — essential for Grade 8.8 electroplated fasteners.
  • ✅ Dual Material Options: Alloy Steel 10B21 or Carbon Steel 35K — both meeting Grade 8.8 requirements, selectable based on application and procurement preference.
  • ✅ RoHS & ELV Compliant Zinc CR3 Finish: Trivalent chromate coating — no hexavalent chromium — meets EU environmental directives.
  • ✅ Full Traceability: Material certificates (MTC), mechanical test reports, hardness records, and salt spray test data available per shipment.
  • ✅ High-Volume Production Capability: Consistent lot-to-lot quality for structural, industrial, and transportation procurement programs.
  • ✅ Wide Size Range: M5 through M20, lengths from 20 mm to 300 mm.
  • ✅ Flexible Packaging: Bulk, box, and custom packaging options available.

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 8.8)
  • DIN 267-11 — Fasteners: technical delivery conditions — electroplated coatings
  • DIN EN ISO 4042 — Fasteners: electroplated coatings (coating thickness, hydrogen embrittlement relief)
  • ISO 9227 — Corrosion tests in artificial atmospheres — neutral salt spray (NSS) test
  • 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 8.8 Zinc CR3 carriage bolts in standard and custom configurations. Please specify the following when placing an inquiry:

  • Thread diameter and pitch (e.g., M10 × 1.5, M12 × 1.75)
  • Nominal length (e.g., 40 mm, 80 mm, 150 mm)
  • Fully threaded or partially threaded shank preference
  • Material preference: Alloy Steel 10B21 or Carbon Steel 35K
  • Required quantity and packaging format (bulk / box / pallet)
  • Certification requirements (PPAP, material certificates, mechanical test reports, hardness records, hydrogen embrittlement relief baking records)

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

FULLERKREG — High-Strength Fasteners for Structural and Industrial Excellence.

Sorry, this collection is empty.
Continue shopping