Welding Rod Sizes: Which Diameter for Which Thickness
The rod diameter you choose determines the amperage range and how much heat goes into the joint. Too large a rod on thin metal burns through. Too small a rod on thick plate wastes time and may not achieve full penetration. Here is how to match them.
The Rule of Thumb
For steel, the rod diameter should be close to the material thickness, up to 3/16 inch. Above that, use 3/16 or larger and make multiple passes.
1/16 inch material: 1/16 or 3/32 inch rod 1/8 inch material: 3/32 or 1/8 inch rod 3/16 inch material: 1/8 or 5/32 inch rod 1/4 inch material: 5/32 or 3/16 inch rod 3/8 inch and above: 3/16 or larger, multiple passes
This is a starting point. Adjust based on position, joint design, and rod type.
Position Changes the Size
The maximum rod size drops when welding out of position. Gravity pulls the weld pool, so you need a smaller, faster-freezing puddle.
Flat: Use any diameter appropriate for the thickness. Horizontal: Drop one size from flat if puddle sags. Vertical-up: Maximum 5/32 inch for most rods. Many welders prefer 1/8 inch. Overhead: Maximum 5/32 inch. 1/8 inch is standard.
For E7018 vertical-up: most pipe welders use 1/8 inch exclusively. The smaller rod gives better puddle control in the weave pattern.
Amperage Ranges by Rod Size
Each rod size has a recommended amperage window. The exact range varies by rod type, but here are the typical ranges for E7018:
3/32 inch: 65-110A 1/8 inch: 110-165A 5/32 inch: 140-220A 3/16 inch: 200-280A 7/32 inch: 260-340A 1/4 inch: 315-400A
Start in the middle of the range and adjust. If the rod sticks, go up. If you are burning through or the bead is too wide, go down. The amperage charts on each electrode page in GageRef give exact ranges by rod type and diameter.
When to Use Larger vs Smaller Rods
Use a larger rod when deposition speed matters, when the joint is thick, when welding flat, and when your machine has enough amperage.
Use a smaller rod when welding thin material, when welding out of position, when you need precise heat control, or when your machine is limited on amperage. A 120-amp machine cannot run a 3/16 inch E7018 properly, use 1/8 inch instead.
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