Product Summary

Longze High-Precision Fine Thread Hex Bolts (ISO 8765 / ISO 8676) are engineered for applications requiring superior adjustment precision, higher stripping resistance, and

better vibration security. Manufactured in Yongnian, China, our fine-pitch bolts offer a larger minor diameter and a lower helix angle compared to standard coarse threads, providing

higher tensile strength and preventing loosening in high-vibration environments. Whether for automotive drivetrains, hydraulic manifolds, or aerospace framing, Longze fine-thread bolts deliver the clamping force and fatigue resistance required for high-stress engineering.

• ✔ Superior Vibration Resistance: The smaller helix angle of the fine thread ($\beta$) provides a natural self-locking effect, making these bolts significantly more resistant to loosening under dynamic loads.

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• ✔ Higher Tensile Strength: Due to the smaller thread depth, fine-thread bolts have a larger tensile stress area, offering approximately 10-15% higher load capacity than coarse threads of the same size.

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• ✔ Micro-Adjustment Precision: Ideal for assembly scenarios requiring fine-tuned tension or positioning, our ISO 8676 bolts ensure consistent movement per revolution.

• Standards: ISO 8765 (Partially Threaded), ISO 8676 (Fully Threaded), DIN 960 / 961.

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• Diameter Range: M8 x 1.0 to M64 x 3.0 (Various fine pitch options).

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• Pitch Options: 0.75mm, 1.0mm, 1.25mm, 1.5mm, 2.0mm.

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• Property Class: Class 8.8, 10.9, 12.9 | Stainless Steel 304 (A2) & 316 (A4).

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• Surface Finish: Black Oxide, Zinc Plated (Clear/Yellow), Geomet, Dacromet, Zinc-Nickel.

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)	Hardness Range
  Class 8.8	Medium Carbon Steel	800 MPa	640 MPa	22 - 32 HRC
  Class 10.9	Alloy Steel (SCM435)	1040 MPa	940 MPa	32 - 39 HRC
  Class 12.9	Alloy Steel (SCM440)	1220 MPa	1100 MPa	39 - 44 HRC
  SS316 (A4-80)	Неръждаема стомана	800 MPa	600 MPa	240 - 320 HV

Standard Cross Arm Dimensions

• Common configurations for standard fine-pitch mechanical assemblies.

• Thread Size (D x P)	Width Across Flats (s)	Head Height (k)	Proof Load (10.9)	Max Torque (12.9)
  M10 x 1.25	16 mm	6.4 mm	63.5 kN	85 Nm
  M12 x 1.25	18 mm	7.5 mm	92.5 kN	150 Nm
  M14 x 1.5	21 mm	8.8 mm	125 kN	240 Nm
  M16 x 1.5	24 mm	10.0 mm	171 kN	370 Nm

Galvanizing & Corrosion Resistance

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

• Surface Treatment	Coating Thickness	Salt Spray Test	Best Application	Thread Clearance
  Black Oxide	N/A	24 - 48 Hours	Internal Engines	6g (Standard)
  Zinc Plated	8 - 12 μm	72 - 144 Hours	General Machinery	6g (Standard)
  Zinc-Nickel	8 - 10 μm	1000+ Hours	Automotive / EV	6g (Precision)
  Dacromet	8 - 12 μm	500 - 1000 Hours	Marine / Outdoor	6g (Precision)

Avoid Pitfalls:

• Thread Galling (Stainless Steel): Fine threads are more prone to "cold welding" or galling. Longze provides specialized anti-galling coatings (PTFE or Moly) to ensure smooth installation of SS316 fine bolts.

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• Hydrogen Embrittlement (Class 10.9): Due to the high surface tension of fine threads, 10.9 bolts must be baked immediately after plating. We implement a strict 8-hour de-embrittlement cycle at 200°C for all electroplated fine-pitch batches.

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• Pitch Identification: A 1.25 pitch looks very similar to 1.5 to the naked eye. We implement 100% thread gauge verification and clearly label every carton to prevent costly onsite mix-ups.

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Perfect Fit Assembly:

• Matched Fine Nuts: We recommend pairing these with Longze Class 10 Fine Thread Hex Nuts (DIN 934 / ISO 8673) to ensure a high-integrity connection that utilizes the full strength of the fine-pitch design.

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• Lubrication is Key: Because fine threads are more susceptible to damage during assembly, we suggest a light lubrication to reduce friction and achieve accurate torque-to-tension conversion.

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Quality Control & Logistics:

• ISO 9001 Certified: 5-step QC including computerized optical sorting for pitch accuracy, tensile testing of heat-treated batches, and salt spray analysis.

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• Sea-Worthy Packaging: Fine-thread bolts are individually sleeved or layer-packed with protective padding to prevent thread-to-thread impact damage during international transport from our Yongnian hub.

• Q: Why use fine thread instead of standard coarse thread? A: Fine threads are stronger in tension, provide better adjustment control, and are significantly more resistant to loosening under vibration—critical for automotive and high-speed machinery.

• Q: Can you supply ISO 8765 in custom lengths? A: Yes. We can manufacture custom shank and thread lengths for specific mechanical clearances using our multi-station cold heading equipment.