What do the first two numbers of a welding electrode refer to?

The first two numbers of a welding electrode indicate its tensile strength, specifically the minimum tensile strength measured in thousands of pounds per square inch (psi). This information is crucial because it helps welders select the appropriate electrode for the materials they are working with, ensuring that the weld will achieve the necessary strength for its application. For example, if the first two numbers are 70, this means the electrode can provide a weld with a minimum tensile strength of 70,000 psi. Understanding tensile strength is fundamental in making informed choices about welding processes, especially when dealing with structural welding or applications that demand specific performance criteria.

The other options relate to different aspects of electrodes but do not pertain to the first two numbers. Diameter refers to the size of the electrode, while length and type of coating are also essential characteristics but are represented in other parts of the electrode classification system.