Product Summary

Longze Heavy-Duty Carriage Bolts (DIN 603 / ASME B18.5) are high-security fasteners designed for timber-to-timber and timber-to-metal connections. Manufactured in

Yongnian, China, our carriage bolts feature a smooth, low-profile dome head that prevents tampering from the outside, paired with a precision-forged square neck that locks into

the base material. Whether for structural wooden bridges, playground equipment, or security fencing, Longze carriage bolts provide the clamping force and aesthetic finish required for heavy-duty construction.

• ✔ Anti-Spin Square Neck: The square neck is forged with sharp, well-defined corners to ensure a positive lock in pre-drilled holes, preventing the bolt from rotating during nut tightening.

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• ✔ Tamper-Resistant Head: The smooth cup head has no drive (no hex or slot), making it impossible to loosen from the exterior—an essential feature for public infrastructure and security gates.

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• ✔ Forged Strength: Our cold-forming process ensures the transition between the cup head and the square neck is structurally reinforced to prevent head-snapping under high-torque assembly.

• tandards: DIN 603, ISO 8677, ASME B18.5 (Step Bolts / Carriage Bolts).

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• Diameter Range: M5 to M24 | 1/4" to 1".

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• Length Range: 12mm to 400mm (Fully threaded or partial thread for thick timber).

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• Material Grade: Carbon Steel (Class 4.8, 8.8) | Stainless Steel 304 (A2) & 316 (A4).

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• Surface Finish: Hot Dip Galvanized (HDG), Zinc Plated (Blue/White/Yellow), Black Oxide, Plain.

Mechanical Properties & Material Standards

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

• Property Class	Vật liệu	Tensile Strength (min)	Yield Strength (min)	Best Application
  Class 4.8	Low Carbon Steel	400 MPa	320 MPa	General Timber / DIY
  Class 8.8	Medium Carbon Steel	800 MPa	640 MPa	Structural Wood / Machinery
  SS304 (A2)	Thép không gỉ	700 MPa	450 MPa	Playground / Food Grade
  SS316 (A4)	Thép không gỉ	800 MPa	600 MPa	Marine / Coastal Decking

Standard Cross Arm Dimensions

• Common angle steel configurations for standard utility pole mounting.

• Thread Size (D)	Head Dia (dk)	Head Height (k)	Neck Width (v)	Neck Height (f)
  M8	20.6 mm	4.8 mm	8.5 mm	5.6 mm
  M10	24.6 mm	5.8 mm	10.5 mm	6.6 mm
  M12	30.6 mm	7.2 mm	12.6 mm	8.7 mm
  M16	38.8 mm	9.3 mm	16.7 mm	12.9 mm

Galvanizing & Corrosion Resistance

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

• Surface Treatment	Coating Thickness	Salt Spray Test	Service Life	Môi trường
  Zinc Plated	8 - 12 μm	72 - 144 Hours	High	Indoor / Furniture
  Hot Dip Galv.	≥ 55 μm	500 - 800 Hours	Maximum	Outdoor / Timber Posts
  SS316 Polished	N/A	1000+ Hours	Lifetime	Marine / High Humidity

Avoid Pitfalls:

• Square Neck Interference: If the square neck (v) is wider than the bolt diameter (D), it requires a specific oversized hole. Longze strictly adheres to DIN 603 tolerances to ensure the neck bites into the material without splitting the wood.

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• Incomplete Threads on HDG: For hot-dip galvanized carriage bolts, we perform oversized nut matching or specialized thread chasing to ensure the nuts spin on smoothly over the 50-80μm zinc layer.

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• Head Concavity: Poorly forged heads can be concave, trapping water and accelerating corrosion. Longze ensures a consistent, convex dome that sheds water effectively in outdoor installations.

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Perfect Fit Assembly:

• Matching Flange Nuts: Pair our carriage bolts with Longze DIN 6923 Flange Nuts to provide a large bearing surface on the back side, preventing the nut from sinking into soft wood.

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• Reinforced Timber Joinery: For heavy structural beams, use our 8.8 High-Strength Carriage Bolts to achieve the necessary clamping force that standard 4.8 bolts cannot provide.

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Quality Control & Logistics:

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• ISO 9001 Certified: 5-step QC including square neck dimension verification, head-to-neck tensile testing, and salt spray analysis for galvanized batches.

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• Sea-Worthy Packaging: Bolts are packed in double-walled 25kg cartons, plastic-lined for moisture protection, and palletized for export from our Yongnian hub.

• Q: Can I use carriage bolts in metal-to-metal joints? A: Yes, but the receiving hole in the first metal plate must be a square punched hole to accommodate the square neck.

• Q: Why do my stainless steel carriage bolts show tea-staining? A: This is often surface contamination from carbon steel tools. For coastal projects, we strictly recommend our SS316 grade with a passivated finish to prevent surface staining.