Selecting the right welding rod is critical to the success of your welding job. You see here before me four different kinds of welding rods. They vary in three important ways. One is diameter from 5/32 to 1/8 to 3/32 to numerical number 6013 in this case, 6011 here, and 7014 here. This last set of welding rods, with the white flux, is actually for welding aluminum. The catch is you have to have an arc welder with DC capability, that is direct current, in order to use these rods to weld aluminum. There are other similar specialty rods for stainless steel, cast iron, bronze, and other metals, but each of them require DC voltage capability on your welder.
A word about welding rod classification. Welding rods come in two classifications, 60XX or 70XX, that is 70 with a suffix or 60 with a suffix. This large rod here is a 7014. The 70 indicates that this is a structural quality welding rod. That is, it can be used in the fabrications of buildings, bridges, or anything else which requires structural rating. The 14 tells us that this rod is best used in a flat position. A 70 series rod provides extremely high strength alloy steel, very smooth welds, very easy slide removal, but working best in a flat position.
The 6011 rod, here 1/8, is an all-purpose rod. The 11 designates that it has a deep gouging arc. It's particularly good on rusty, or dirty, or painted metals and will also work in all positions. This rod is considered by some people to be difficult to use, but it's my favorite as it's the most versatile and can be utilized in the most number of possible positions and situations.
This small 3/32 rod is designated 6013. The 60 also designates the utility nature of this rod. The 13 means that it can be used in all positions but is best used flat. The 6013 rods are also what we call contact rods. That is, when you're welding you have more of a sense of physical connection between the rod and the material itself. The 6013 and 6014 are considered to be one of the easiest welding rods to use.
I've only shown you four of dozens of different types of welding rods that are used for all kinds of different purposes. A good rule of thumb is to always check the manufacturer's recommendations regarding use, position, voltage range, and purpose of the welding rods.