Round Head Square Neck Bolt

Round Head Square Neck Bolt — Product Description

The Round Head Square Neck Bolt is a fastener with a semi-spherical head and a square-section neck, commonly known as a “carriage bolt.” Its working principle is as follows: the square neck is inserted into a square hole or slot in the mating part, forming a mechanical interlock that prevents the bolt from rotating during tightening on the nut side. This enables one-person, single-side operation to complete the fastening. Products are generally manufactured to GB/T 12-2013. Thread sizes cover M6 to M20, with product grade C. Common materials include carbon steel and stainless steel.

1. Product Features

• Unique anti-rotation design. The square neck directly beneath the head is the core feature. During installation, the square neck fits into a square hole or slot in the mating part, forming a mechanical interlock that effectively prevents the bolt from rotating during tightening.
• Smooth round head. The head is semi-spherical with no driving structure such as a cross recess or hex socket. This design is aesthetically pleasing, resists snagging on clothing or injuring personnel, and offers a degree of tamper resistance.
• Standards and specifications. The current Chinese national standard is GB/T 12-2013, which specifies thread sizes from M6 to M20 and product grade C. The German standard DIN 603 is also a common reference.
• Common materials and treatments. Common materials include carbon steel (such as Q235 and No. 45 steel) and stainless steel (such as 304). Carbon steel parts are typically finished with zinc plating, Dacromet, or other surface treatments for rust prevention.

2. Product Advantages

• Convenient and efficient installation. The anti-rotation feature of the square neck allows a single person to complete the locking operation from one side, without using a tool on the head. This significantly improves assembly efficiency.
• Safe and tamper-resistant. The smooth round head has no sharp edges, reducing the risk of scratches to personnel or materials. It is suitable for exposed assembly applications. Additionally, the absence of a driving structure on the head provides inherent tamper resistance.
• Stable and reliable connection. The tight fit between the square neck and the hole or slot effectively resists vibration, prevents bolt loosening, and provides a stable connection.
• Gentle on base material. The round head design results in lower stress concentration on the contact surface, making it especially suitable for softer materials such as wood, and less likely to crush the surface.

3. Applications

• Wood construction engineering. Widely used in wooden houses, prefabricated houses, wooden furniture, scaffolding, and for joining wood to metal components.
• Vehicle and ship manufacturing. Commonly used in truck cargo boxes, trailers, ship assembly, and vehicle chassis applications.
• Building and decoration. Suitable for installation of dry-hung stone curtain walls, and for applications requiring concealed or tamper-resistant fastening.
• General machinery and equipment. Also applied in mechanical equipment, electronic equipment, communication equipment, medical equipment, and the aviation industry.