Final answer:
The first bead when welding two pieces of metal is called a root pass, providing the foundation for subsequent layers and ensuring a strong weld.
Step-by-step explanation:
The first bead made when welding two pieces of metal together is called a root pass. It is the fundamental first layer of weld material applied at the joint between the two metal pieces. The root pass is crucial because it provides the foundation for all subsequent layers or passes, ensuring there is penetration into the base material for a strong weld. After the root pass, welders may perform additional passes, such as the fill pass to add more material, and the cover pass or cap pass to provide a clean finish.