What type of bolt is used to fasten guard rails to the running?

The correct answer is that guard rails are typically fastened to the running using a standard bolt. Standard bolts are commonly used in railway applications because they provide a strong and secure connection. These bolts are designed to withstand the forces and vibrations encountered in rail operations, ensuring stability and safety.

In the context of railway construction, it is important to use fasteners that are reliable and can endure environmental conditions, along with the mechanical stresses assigned to them. Standard bolts meet these requirements, making them suitable for securing guard rails to the running.

Other types of bolts, while having specific applications, may not offer the same level of performance for this particular task. For instance, self-locking bolts are designed for applications where vibration loosening is a concern but may not be needed for guard rail installation. Hex bolts are also used in various applications but may not be the standard choice for this specific purpose. Round head bolts are oriented differently and are typically not suited for fastening guard rails due to their design.

Thus, the selection of standard bolts for fastening guard rails aligns with industry practices and ensures the safety and integrity of the rail system.