Most rods that one runs across at the farm supply store will be labeled something like this: E 6011 or, perhaps, E 7020. The 'E' means that it is an electrode suitable for arc welding. The following two numbers indicate the tensile strength of the material in the rod when the weld is stress relieved. '60' stands for 60,000 psi, '70' for 70,000 psi, etc. The next number, a one, two, or three, indicate the position of the joint the electrode is designed to weld. For example, an electrode numbered XX1X will weld in all positions. A XX2X will weld butt and fillet joints in the flat or horizontal position. XX3X is recommended for flat position welds only. The last number is an indicator of the power supply, type of covering, type of arc penetration and presence of iron powder. The whole article: http://www.ytmag.com/articles/artint160.