ISO 8677 is the international standard for Bu lông đầu vuông cổ cốc, widely recognized across global markets. Commonly known as "Carriage Bolts," this standard specifies the dimensional characteristics for metric bolts featuring a large, rounded head and a square neck to prevent rotation during tightening.

As the ISO equivalent to the German DIN 603, ISO 8677 ensures global interchangeability. The square neck is designed to lock into the substrate (typically timber or pre-punched metal), allowing the fastener to be secured using only a nut and wrench from the opposite side. Its smooth, low-profile head makes it ideal for safety-conscious applications like playground equipment and public infrastructure.

The technical focus of ISO 8677 is the Self-Locking Geometry. The "cup" or mushroom head provides a decorative finish while distributing load across a wide area ($d_k$), minimizing surface damage to wood or soft composites. The square neck ($v$) is the mechanical driver; it must be fully engaged to prevent the bolt from spinning, ensuring high torque can be applied to achieve a secure clamp without requiring access to the bolt head.