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ANSI/ASME B18.5 Round Head Square Neck Bolt

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ANSI/ASME B18.5 Round Head Square Neck Bolts combining a smooth, rounded head with a square neck to prevent rotation during installation. This unique design ensures secure seating in square-shaped recesses or mating components, eliminating slippage even under extreme torque. Manufactured to ANSI/ASME B18.5 standards, these bolts deliver consistent dimensions and mechanical properties, making them ideal for assemblies requiring both aesthetic smoothness and anti-rotational stability.

In automotive engineering, ANSI/ASME B18.5 bolts are commonly used in components exposed to high vibration and torsional stress. Their square neck feature is particularly advantageous in drivetrain systems, axle housings, and heavy-duty suspension linkages, where rotational resistance is critical to maintaining structural integrity. The rounded head design also reduces protrusion risks, making them suitable for automotive applications requiring streamlined profiles, such as underbody panels or transmission mounts.


Key Advantages for Your Applications:

  • Positive Anti-Rotation: The square neck design effectively prevents bolt rotation, ensuring joint integrity under high torque and vibration.
  • Aesthetic Smoothness: The rounded head provides a clean and streamlined appearance, suitable for visible automotive components.
  • Consistent Dimensions & Properties: Manufactured to ANSI/ASME B18.5 standards, guaranteeing dimensional accuracy and reliable mechanical performance.
  • Enhanced Structural Integrity: Prevents loosening and maintains the clamping force of critical automotive joints.
  • Reduced Assembly Time: The self-locking feature can simplify the assembly process by eliminating the need for additional anti-rotation hardware.
  • Minimized Damage Risk: The rounded head reduces the potential for snagging or damage to surrounding components.

Ideal for:

  • Drivetrain Systems: Securing components where high torsional stress and vibration are present, such as transmission mounts and axle housings.
  • Heavy-Duty Suspension Linkages: Providing reliable, non-rotating connections in critical suspension components.
  • Underbody Panels: Offering a low-profile, secure fastening solution that minimizes protrusion.
  • Transmission Mounts: Ensuring stable and vibration-resistant mounting of the transmission.
  • Seating Assemblies: Providing secure and aesthetically pleasing fastening for seat frames and mechanisms.
  • Body Panels: Securing panels where a smooth exterior finish is desired along with robust fastening.
  • Agricultural and Construction Equipment: Applications requiring resistance to rotation in demanding environments.



Product Name Standard Material & Finish Diameter (Shank) Length (Shank)
Round Head Square Neck Bolt ASTM A449 Grade 5 Carbon Steel, Zinc Plated 1/2" (12.7mm) 2" (50.8mm)
Round Head Square Neck Bolt ASTM A449 Grade 8 Alloy Steel, Hot-Dip Galv 5/8" (16mm) 3" (76.2mm)
Round Head Square Neck Bolt ASTM A449 AISI 304 Stainless Steel, Plain 3/4" (19.05mm) 4" (101.6mm)
Round Head Square Neck Bolt DIN 603 8.8 Steel, Zinc Flake Coated M12 40mm
Round Head Square Neck Bolt DIN 603 10.9 Steel, Dacromet Coated M16 60mm
Round Head Square Neck Bolt DIN 603 A2-70 Stainless Steel M20 80mm
Round Head Square Neck Bolt ISO 7412 Class 8.8 Steel, Electrogalvanized M24 100mm
Round Head Square Neck Bolt ISO 7412 Class 10.9 Steel, Phosphated M30 120mm
Round Head Square Neck Bolt GB/T 1228 40Cr Steel, Hot-Dip Galvanized M36 150mm
Round Head Square Neck Bolt ASME B18.5 ASTM A325 Type 1, Plain 1" (25.4mm) 6" (152.4mm)
Round Head Square Neck Bolt ASME B18.5 ASTM A490, Xylan Coated 1-1/4" (31.75mm) 8" (203.2mm)
Round Head Square Neck Bolt JIS B1180 SCM435 Alloy Steel, Zinc Plated M10 30mm
Round Head Square Neck Bolt JIS B1180 SUS316 Stainless Steel M14 50mm
Round Head Square Neck Bolt BS 3692 Grade 8.8 Steel, Geomet Coated M18 70mm
Round Head Square Neck Bolt SAE J429 Grade 2 Steel, Plain 7/16" (11.11mm) 1-1/2" (38.1mm)
Round Head Square Neck Bolt SAE J429 Grade 5 Steel, Zinc-Nickel 3/4" (19.05mm) 5" (127mm)



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Zhejiang Zhongrui Auto Parts Co., Ltd.
Zhejiang Zhongrui Auto Parts Co., Ltd.
As China Automotive ANSI/ASME B18.5 Round Head Square Neck Bolt Suppliers and Custom ANSI/ASME B18.5 Round Head Square Neck Bolt Factory.
Zhejiang Zhongrui Auto Parts Co., Ltd. was founded in 1986. The original unit is located in Ruian City, one of the birthplaces of Wenzhou's economic model, and is located in Tangxia, the "Auto Parts Capital of China". In 2004, in order to further expand its production scale, the company The industrial park in Jiaxing City, Zhejiang, which is located in a very advantageous location, acquired new land and built a modern production plant and office building. The company covers an area of ​​36,237 square meters, with a factory area of ​​20,000 square meters. The company's fixed assets are 130 million yuan.
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