Every stick welding electrode follows the AWS (American Welding Society) EXXXX classification system. Once you understand what each digit means, you can pick the right rod for any joint, position, or base metal without guessing.
The system is straightforward. The “E” means electrode. The next two digits tell you the minimum tensile strength of the deposited weld metal in thousands of PSI. The third digit indicates which positions the rod can weld in. The fourth digit identifies the flux coating type, which determines current type, polarity, penetration profile, and arc characteristics.
How the EXXXX Numbering System Works
Take the most common structural rod, the E7018:
- E = Electrode (always present)
- 70 = 70,000 PSI minimum tensile strength
- 1 = All-position capable (flat, horizontal, vertical, overhead)
- 8 = Low-hydrogen potassium, iron powder coating. AC or DCEP.
The last digit is where most of the practical information lives. It tells you the flux chemistry, which controls everything from penetration depth to slag behavior to whether the rod runs on AC.
Position Digit (Third Digit)
The third digit only has two practical values for mild steel electrodes:
| Third Digit | Positions Allowed | Examples |
|---|---|---|
| 1 | All positions (flat, horizontal, vertical, overhead) | E6010, E6011, E6013, E7018 |
| 2 | Flat and horizontal only | E7024 |
Rods with a “2” in the third position have heavy iron powder coatings that produce a large, fluid weld pool. Gravity pulls that pool out of position, so they’re restricted to flat and horizontal joints.
Coating/Current Digit (Fourth Digit)
This is the digit you need to memorize. It controls the rod’s behavior more than any other factor.
| Last Digit | Coating Type | Current/Polarity | Penetration | Common Rods |
|---|---|---|---|---|
| 0 | High cellulose sodium | DCEP only | Deep, digging | E6010 |
| 1 | High cellulose potassium | AC or DCEP | Deep, digging | E6011 |
| 2 | High titania sodium | AC or DCEN | Medium | E6012 |
| 3 | High titania potassium | AC, DCEP, or DCEN | Shallow | E6013 |
| 4 | Iron powder, titania | AC, DCEP, or DCEN | Medium | E7024 |
| 5 | Low hydrogen sodium | DCEP only | Medium | E7015 |
| 6 | Low hydrogen potassium | AC or DCEP | Medium | E7016 |
| 8 | Low hydrogen potassium, iron powder | AC or DCEP | Medium | E7018 |
Flux Coating Types Explained
The coating on a stick electrode does three critical jobs at once: it generates shielding gas to protect the molten weld pool from atmospheric contamination, it produces slag that covers and protects the cooling bead, and it adds alloying elements and deoxidizers to the weld metal. Different coating chemistries create dramatically different welding characteristics.
Cellulosic Coatings (Digits 0 and 1)
Cellulosic coatings contain up to 30% cellulose (wood pulp, paper). When this organic material burns, it produces a large volume of shielding gas, mostly hydrogen and carbon monoxide. The gas-heavy shield and minimal slag create a fast-freeze weld pool with deep penetration.
Cellulosic rods are the choice for pipeline root passes, dirty steel, and field repairs where you need to burn through rust, mill scale, and paint. The trade-off is more spatter, a rougher bead appearance, and a hotter arc that demands more skill to control.
E6010 uses a sodium-based binder and requires DCEP. E6011 swaps in potassium, which ionizes more easily and allows the rod to run on AC. If your machine outputs clean DC, E6010 gives slightly better penetration and arc control. If you’re running an AC buzz box, E6011 is your alternative.
Rutile (Titania) Coatings (Digits 2, 3, and 4)
Rutile coatings are based on titanium dioxide (TiO2). They produce a smooth, quiet arc with low spatter, a fluid slag that peels off easily, and good bead appearance. Penetration is moderate to shallow.
E6013 is the most common rutile rod. It’s the standard “learner” electrode because it’s forgiving on arc length, starts easily, and runs on any polarity. The downside is shallow penetration, which limits its use on structural joints and thick material.
E7024 adds heavy iron powder to a rutile base. The iron powder increases deposition rate by 30-50% compared to standard rods. It’s a “drag” rod for production flat fillet welding. Lay it on the joint, maintain contact, and drag. The weld practically runs itself.
Basic/Low-Hydrogen Coatings (Digits 5, 6, and 8)
Low-hydrogen coatings use calcium carbonate and calcium fluoride as their primary ingredients. The critical feature: they contain less than 0.6% moisture by weight when properly manufactured and stored. That low moisture content means very little hydrogen enters the weld pool.
Hydrogen in a weld is the primary cause of hydrogen-induced cracking (also called cold cracking or delayed cracking). This is especially dangerous in medium-carbon steels, high-strength steels, and thick sections where residual stresses are high. Low-hydrogen electrodes prevent this failure mode.
E7018 dominates this category. It’s the standard structural electrode specified by AWS D1.1 (Structural Welding Code - Steel) and most building codes. The iron powder in its coating (digit 8 vs digits 5 or 6) adds deposition rate and makes the arc smoother.
The catch: low-hydrogen coatings are hygroscopic. They absorb moisture from the air. Once exposed, rods must be stored in a rod oven at 250-300F (120-150C). Rods left out overnight in humid conditions can absorb enough moisture to cause porosity and cracking. See 7018 Rod Storage and Handling for complete storage requirements.
Iron Powder Coatings
Iron powder isn’t a separate coating category but an additive blended into rutile or low-hydrogen coatings. The iron powder melts and adds to the weld deposit, boosting deposition rate. Rods with “iron powder” in their designation (E7018, E7024) deposit more weld metal per rod than their non-iron-powder counterparts (E7016, E6013).
Iron powder content ranges from about 10% (E7018) up to 50% (E7024). Higher iron powder means faster fill rates but a larger, more fluid weld pool that’s harder to control out of position.
How to Read a Welding Rod Label
Every electrode package includes information beyond just the EXXXX number. Here’s what you’ll find on a typical container:
AWS Classification
The full AWS designation appears on every container. For mild steel electrodes, the governing specification is AWS A5.1 (Carbon Steel Electrodes for Shielded Metal Arc Welding). You’ll see this printed as “AWS A5.1 E7018” or similar.
Other AWS electrode specifications you might encounter:
| AWS Spec | Covers | Example Electrodes |
|---|---|---|
| A5.1 | Carbon steel electrodes | E6010, E6011, E6013, E7018, E7024 |
| A5.4 | Stainless steel electrodes | E308L-16, E309L-16, E316L-16 |
| A5.5 | Low-alloy steel electrodes | E7018-A1, E8018-B2, E9018-B3 |
| A5.15 | Cast iron electrodes | ENi-CI, ENiFe-CI |
Suffix Designations
Some rods have additional suffixes after the four-digit classification:
- -1 = Improved toughness (e.g., E7018-1 meets Charpy impact requirements at -50F)
- -H4, -H8, -H16 = Maximum diffusible hydrogen level (H4 = max 4 ml/100g, H8 = max 8 ml/100g)
- -M = Meets military specification
- -A1, -B2, -C3 = Alloy content for low-alloy electrodes (A1 = 0.5% Mo, B2 = 1.25%Cr-0.5%Mo)
For code work, the hydrogen designator matters. AWS D1.1 requires H8 or better for many structural applications. If your welding procedure specification (WPS) calls for E7018-H4R, you need that exact designation on the rod container.
The “-R” Suffix
The “-R” at the end of designations like E7018-H4R means the electrode meets moisture-resistance requirements for the coating. These rods can be exposed to ambient conditions for up to 9 hours (per AWS A5.1) before requiring reconditioning. Standard E7018 without the -R suffix should be kept in the rod oven whenever possible.
Selecting the Right Rod for the Job
Electrode selection comes down to five factors:
1. Base Metal Match
Match the electrode’s tensile strength to the base metal. For A36 structural steel (36,000 PSI yield, 58,000-80,000 PSI tensile), E70XX electrodes provide an appropriate overmatching weld. For higher-strength steels, you’ll need E80XX or E90XX electrodes from AWS A5.5.
2. Joint Condition
Clean, prepped steel opens up your options. Rusty, oily, painted, or galvanized steel narrows them fast. Cellulosic rods (6010, 6011) burn through contamination better than any other type. Low-hydrogen rods (7018) are sensitive to surface contamination and need clean metal to perform.
3. Welding Position
All-position rods (third digit = 1) work everywhere. But “works” and “works well” are different things. For vertical-up welding, 7018 and 6010 are the standards. For overhead, 7018 at reduced amperage is typical. For flat production work, E7024 deposits metal much faster than all-position rods. See the amperage chart for position-specific settings.
4. Machine Output
An AC-only buzz box can only run rods rated for AC: E6011, E6013, E7018, E7024. It cannot run E6010 (DCEP only). If you have a DC inverter, you can run anything. Always check the fourth digit to confirm AC capability.
5. Code Requirements
Structural work governed by AWS D1.1 typically requires low-hydrogen electrodes (E7018 or equivalent). The WPS for the job specifies the exact electrode classification, and deviating without engineering approval violates the code.
Rod Diameter Selection
Bigger rods deposit more metal per hour but need more amperage and produce more heat input. Smaller rods give you more control but fill slower.
| Rod Diameter | Typical Use | Material Thickness Range |
|---|---|---|
| 3/32" (2.4mm) | Thin material, root passes, overhead, vertical | 16 gauge to 3/16" |
| 1/8" (3.2mm) | Most common all-around size | 1/8" to 3/8" |
| 5/32" (4.0mm) | Heavier plate, flat/horizontal fill passes | 1/4" to 1/2" |
| 3/16" (4.8mm) | Heavy plate, high-deposition flat work | 3/8" and up |
A good rule of thumb: the rod diameter shouldn’t exceed the thickness of the thinnest piece you’re joining. For vertical and overhead work, drop one diameter size below what you’d use for flat welding on the same thickness.
Specialty Electrodes Worth Knowing
Beyond the five common mild steel rods, several specialty electrodes solve specific problems:
Stainless Steel (AWS A5.4)
Stainless electrodes follow a slightly different naming system. E308L-16 breaks down as: E = electrode, 308 = alloy type (matches 304 stainless base metal), L = low carbon (for corrosion resistance), 16 = coating/current type (AC or DCEP). Match the filler alloy to the base metal, and use the -L variant for anything that will see corrosive service.
Cast Iron (AWS A5.15)
ENi-CI (99% nickel) and ENiFe-CI (55% nickel, 45% iron) are the standard cast iron repair electrodes. Nickel is soft, machinable, and compatible with cast iron’s high carbon content. See Stick Welding Cast Iron for technique details.
Hardfacing
Hardfacing electrodes deposit wear-resistant alloys onto parts subject to abrasion, impact, or erosion. These don’t follow the EXXXX system. They’re classified under AWS A5.13 and A5.21 with designations like EFe1, EFeCr-A1, and ECoCr-A. Common in mining, agriculture, and earthmoving equipment repair.
Common Mistakes in Rod Selection
Using 6013 for structural work. E6013’s shallow penetration and 60,000 PSI rating make it unsuitable for structural connections. It’s a practice and light-fabrication rod.
Running 6010 on an AC machine. E6010 requires clean DCEP. It won’t stabilize on AC. Use E6011 instead.
Ignoring storage on 7018. Moisture-contaminated 7018 rods cause porosity and hydrogen cracking. This is the single most common quality problem in structural stick welding. Store opened packages in a rod oven at 250-300F.
Oversizing the rod. A 3/16" rod on 1/8" plate will blow through. Match rod diameter to material thickness and position. When in doubt, go one size smaller.
Mixing rod types in a single joint. Don’t start a root pass with 6010 and fill with 6013. The fill passes need at least as much tensile strength as the root. A 6010 root with 7018 fill is standard practice. A 7018 root with 6013 fill is a code violation.
Troubleshooting Rod Selection Issues
Excessive spatter with 6010/6011: These rods produce more spatter by design. Reduce your arc length to one rod diameter. If spatter is unacceptable, switch to E7018 (provided the metal is clean).
Porosity with 7018: Almost always a moisture problem. Check rod storage. Also check for surface contamination, oil, or paint on the base metal.
Rod sticking on start: Amperage is too low, or you’re hesitating on the strike. Use a scratch start motion, and increase amps by 5-10 until the rod ignites cleanly.
Slag inclusions: Incomplete slag removal between passes, or too wide a weave trapping slag at the toes. Chip and wire-brush each pass completely before the next. See Stick Welding Common Defects for detailed defect analysis.
Arc wanders or feels unstable on AC: Some rods are designed for DC only (E6010, E7015). Verify your rod is AC-rated by checking the fourth digit. Also check that your AC machine provides adequate open-circuit voltage (OCV). Most AC rods need at least 50V OCV to maintain a stable arc.