Electrodes for welding have numbers stamped on them to identify the type and characteristics of the electrode as specified by the American Welding Society (AWS). The AWS number gives the welder complete information about the welding rod.
Numbers for mild or low alloy steel electrodes begin with an "E" prefix (meaning "electrode") followed by a four or five-digit number in most cases. Rods come in sizes from 1/16 to 5/16, so a typical number would indicate a 1/8 inch E10011 rod.
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The tensile strength of the electrode is indicated in thousand-pound increments by the first two digits of a four-digit number and the first three of a five-digit number. If the number following the "E" is four digits, and the first two are 50, then the electrode is 50,000 pounds per square inch (psi) minimum tensile strength. If it's a five-digit number and the first three are 120, then the electrode is 120,000 psi.
The next-to-last digit indicates what position the rod can be used in. A "1" indicates all positions, "2" indicates flat and horizontal positions and a "3" is for flat welding.
The last digit tells what type of coating is on the electrode and type of current as follows: 1=cellulose sodium DC+, 2=cellulose potassium AC, DC+ or DC-, 3=titania sodium AC or DC-, 4=iron powder titania AC, DC+ or DC-, 5=low hydrogen sodium DC+, 6=low hydrogen potassium AC or DC+, 7=iron powder iron oxide AC, DC+ or DC-, 8=iron powder low hydrogen AC or DC+.
Extra Numbers and Letters
Special-purpose welding rods may have extra letter and number combinations. The first letter-number combination indicates the chemistry of the weld and will look like A1, B1, B2, B3. After that will come an H number, which indicates how much hydrogen will be diffused when you use the rod. Finally, if the number ends in an "R" it means the rod resists moisture.