Their are many types of welding electrodes. They are grouped according to the matrix used to hold the ingredients and/or the type of metal to be welded. Steel electrodes are classed in 3 types, 1 mild steel, 2 medium tensile steel and 3 hi-tensile steel. Mild steel are used to weld mild steel surprise!! and have a tensile strength of 60,000 psi. +/-. Some types are 6010 - 6011 - 6013 etc. Medium tensile fall into the 70,000 to 80,000 psi range and can be 7016 - 7018 etc. or 8016 - 8018 - 8020 - 8024 etc. High tensile run 90,000 psi. and up. ie: 9018, 10018, 11018, 12018 and have the equvilent tensile strength (psi = pounds per square inch). A CLUE the last number indicates what position you can weld in. Flat, horizontal, vertical up, overhead. 1 = all position 2 = flat and horizontal 3 = flat only 4 = all plus vertical downhand. Their are many types of metal produced from stainless steel to tungsten carbide. Not all can be welded. Some have to be brazed or silver soldered. Charts can be obtained to tell you what electrode or process to use in almost any situation. Or ask your welding supplier.