Welding electrodes are metal wires with baked on chemical coatings. The rod is used to sustain the welding arc and to provide the filler metal required for the joint to be welded. The coating protects the metal from damage, stabilizes the arc, and improves the weld. The diameter of the wire, less the coating, determines the size of the welding rod. This is expressed in fractions of an inch such as 3/32", 1/8", or 5/32." The smaller the diameter means it requires less current and it deposits a smaller amount of filler metal.