Base metal thickness

As a rule, you would select a rod that is a size thinner than the base metal. For example, if the base metal thickness is 1/8″, use a 3/32″ rod. This works well on thicknesses up to 3/16” and for standard welds like a one-side single-pass butt weld.

Of course, this rule is not hard and fast since many welding professionals select a rod diameter that is half as thick as the base metal, and they get excellent results. However, if you go with a rod much thinner than that, you risk having a low metal deposition rate.

Choosing a rod with the same diameter as the base metal’s thickness could cause the heat to blow through the metal and create excessive warping. Some novice welders mistakenly pick a rod thicker than the base metal, resulting in too much heat in the joint, making welding nearly impossible.

One exception to the rule applies to very thin metals. For instance, if you are welding 17-gauge (1.4mm) sheet metal, the smallest rod would be 1/16″ (1.6 mm). However, stick welding thin metals is challenging, requiring much experience and giving unsatisfactory results. Veteran welders sometimes use thicker rods on thinner metals since narrow rod diameters are harder to find and costlier.

Also, when the base metal is thicker than 3/16″, it helps to bevel the joint for full penetration and weld it with common-sized rods.