Product Summary

Longze High-Strength Carriage Bolts (DIN 603 / ASME B18.5) are specialized fasteners featuring a smooth, rounded head and a precision-forged square neck that prevents

rotation during tightening. Manufactured in Yongnian, China, our carriage bolts are designed for one-sided installation in timber, metal-to-wood, and solar mounting systems.

Whether for securing outdoor fencing, heavy-duty shelving, or solar panel frames, Longze carriage bolts provide the anti-theft security and sleek profile required for high-visibility structural joints.

• ✔ Integrated Anti-Rotation Square Neck: The precision-forged square section under the head locks into a pre-punched hole, allowing for secure tightening with a single wrench from the nut side.

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• ✔ Flush-Fit Aesthetic Head: The low-profile "Cup Head" provides a smooth surface that eliminates snagging hazards and offers a cleaner, more professional finish compared to standard hex bolts.

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• ✔ Heavy-Duty Corrosion Resistance: Available in both Hot Dip Galvanized (HDG) for infrastructure and SS304/SS316 for marine environments, ensuring a service life exceeding 25 years.

• Standards: DIN 603 (Metric), ASME B18.5 (Imperial / Round Head), ISO 8677.

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• Diameter Range: M5 to M20 | 1/4" to 3/4".

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• Length Range: 20 mm to 300 mm.

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• Property Class: Class 4.8, 8.8 | Grade 2, 5 (ASME) | Stainless Steel 304 / 316.

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• Surface Finish: Hot Dip Galvanized (HDG), Zinc Plated, Black Oxide, Passivated.

Mechanical Properties & Material Standards

• Matching the steel grade to the structural requirements of the transmission line.

• Property Class	Материал	Tensile Strength (min)	Yield Strength (min)	Best Application
  Class 4.8	Low Carbon Steel	420 MPa	340 MPa	Timber / Furniture
  Class 8.8	Medium Carbon Steel	800 MPa	640 MPa	Solar Racking / Steel
  SS304 (A2)	Нержавеющая сталь	700 MPa	450 MPa	Food Grade / Outdoor
  SS316 (A4)	Нержавеющая сталь	800 MPa	600 MPa	Marine / Coastal

Standard Cross Arm Dimensions

• Common dimensions for standard (DIN 603) metric carriage bolts.

• Thread Size (D)	Head Dia (dk)	Head Height (k)	Square Width (f)	Square Height (v)
  M6	16.55 mm	3.88 mm	6.48 mm	4.60 mm
  M8	20.65 mm	4.88 mm	8.58 mm	5.60 mm
  M10	24.65 mm	5.38 mm	10.58 mm	6.60 mm
  М12	30.65 mm	6.95 mm	12.70 mm	8.75 mm

Galvanizing & Corrosion Resistance

• Ensuring 30+ years of service life in corrosive environments.

• Surface Treatment	Process	Salt Spray Test	Service Life	Среда
  Zinc Plated	Electrolytic	72 - 144 Hours	High	Indoor / Dry
  Hot Dip Galv.	Thermal Bath	500 - 800 Hours	Maximum	Solar PV / Outdoor
  Black Oxide	Chemical	24 - 48 Hours	Low	Interior Design
  SS316 Polished	Passivated	1000+ Hours	Lifetime	Marine / Coastal

Avoid Pitfalls:

• Square Neck "Cam-Out": If the square neck isn't deep enough or is too tapered, it will strip the hole in soft timber. Longze uses High-Pressure Cold Heading to ensure sharp, 90° corners on every square neck.

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• Nut Jamming on HDG Bolts: For hot-dip galvanized carriage bolts, the zinc layer can interfere with thread tolerances. We recommend using Longze 6AZ (Oversized) Hex Nuts to guarantee a smooth, reliable fit.

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• The "Flat Head" Trap: Some low-quality suppliers produce heads that are too thin, causing them to pull through the material. Our heads strictly follow DIN 603 dk/k standards for maximum surface support.

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Perfect Fit Assembly:

• Matched Flange Nuts: Pair our 8.8 grade carriage bolts with Longze DIN 6923 Flange Nuts for a unified, high-torque joint in solar mounting structures.

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• Installation Tip: For timber, use a hammer to seat the square neck into the wood before tightening the nut; this prevents the bolt from spinning and damaging the hole.

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Quality Control & Logistics:

• ISO 9001 Certified: 5-step QC including computerized optical sorting for head and neck dimensions, thread gauge verification, and salt spray analysis.

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• Sea-Worthy Packaging: Bolts are packed in plastic-lined 25kg cartons, then secured in reinforced wooden crates to ensure no thread damage or flash rust during export from our Yongnian hub.

• Q: Can you provide fully-threaded carriage bolts? A: Yes, we can manufacture DIN 603 with full threads for shorter lengths or partial threads for longer structural bolts.

• Q: Do you offer ASME B18.5 in Grade 5? A: Absolutely. We supply Grade 5 (High Tensile) carriage bolts for North American infrastructure projects with UNC or UNF threads.