Fillet welds make up most of the welds made in fabrication, and every one of them is run in a position. The codes 1F, 2F, 3F, and 4F are how prints, procedures, and weld tests tell you where that joint will sit, which decides how gravity acts on the puddle and how you have to run the bead. A fillet in the flat position practically lays itself in. The same joint overhead will punish a long arc or a slow hand in a hurry. The notation only takes a minute to learn, but knowing what each position demands is what keeps your leg sizes even and your welds passing inspection. In this guide, we are going to break down what the fillet position codes mean, walk through 1F, 2F, 3F, and 4F one at a time, look at how they factor into qualification, and cover the habits that keep fillets clean in every position.
In these codes, the number indicates the weld position, and the letter indicates the weld type. The letter F stands for fillet, and G stands for groove, so 2F is a fillet weld in the horizontal position and 2G is a groove weld in the same position. The numbers run the same way for both: 1 is flat, 2 is horizontal, 3 is vertical, and 4 is overhead. Pipe adds a few more, covered below. If you already know the groove weld positions, you already know the numbering.
The definitions come from the American Welding Society. AWS A3.0 defines the terms, and codes like AWS D1.1, Structural Welding Code – Steel, use diagrams that show each test position with tolerance bands for how far the joint can rotate or tilt before it becomes a different position. Those bands are what make the system work in the real world. A plate that is a few degrees off level is still flat. One that has rolled 45 degrees is not.
What the number is really describing is the relationship between the weld axis, the weld face, and gravity. In 1F, gravity pulls the molten metal straight into the root. In 2F, it pulls the puddle down toward the bottom plate. In 3F, it pulls along the length of the weld. In 4F, it pulls the puddle out of the joint entirely. Every technique change from one position to the next is an answer to that one problem. The broader system, including groove positions, is covered in our guide to welding positions, so this post stays on fillets.
Each position asks for a different setup, and the setup is most of the battle. Here is what changes as the joint moves off the table.
| Welding Position | Description | Key Techniques | Common Challenges |
| 1F – Flat | Joint positioned in a V-shape, allowing the weld pool to settle naturally into the root. | Use higher heat and faster travel speeds while maintaining even fusion on both legs. | Uneven leg sizes and undercut from excessive heat or poor electrode positioning. |
| 2F – Horizontal | Weld runs horizontally along a T-joint between vertical and horizontal plates. | Start with a 45° work angle, adjusting slightly toward the vertical plate to balance the puddle. | Undercut on the upper toe and overlap on the lower toe due to gravity. |
| 3F – Vertical | Weld runs vertically up or down the joint. | Use vertical-up for stronger penetration, controlled weaving, and pauses at the toes. | Sagging weld pools and lack of fusion, particularly with downhill welding. |
| 4F – Overhead | Welding takes place underneath the joint, with gravity pulling molten metal downward. | Maintain a tight arc, smaller weld pool, and steady travel speed. | Sagging, spatter, falling molten metal, and increased safety risks. |
Fillet welding positions also apply to pipe, with a few differences based on pipe orientation and rotation:
The 5F position is particularly important for pipe welders because it requires transitioning between overhead, vertical, and flat welding without rotating the pipe. It is commonly used for socket fittings, slip-on flanges, and other pipe attachments that cannot be repositioned.
Every welder qualification test is performed in a specific position, which determines the positions a welder can work in. The rules differ a bit between codes, but the logic is the same: a harder position qualifies you for easier ones, and the flat position qualifies you only for flat.
Under AWS D1.1, fillet weld qualifications depend on the test position:
Groove weld qualifications can also cover corresponding fillet positions, which is why many shops use 3G and 4G tests instead of separate fillet tests. Fillet qualification typically involves a break test and macroetch examination by welding inspectors to evaluate fusion, weld size, and defects such as porosity.
Pipe welding follows similar principles. Under ASME Section IX, a 5F test can qualify welders for flat, vertical, and overhead fillet positions.
The AWS Certified Welder program records qualifications based on the welding procedure and position tested. For welders pursuing structural welding or pipeline work, understanding these requirements is essential. An “all-position” qualification means demonstrating the ability to weld beyond the easiest positions.
Welding clean fillets in different positions comes down to consistent technique and proper adjustments. The fundamentals stay the same, but heat, angles, and puddle control must change with the position.
Ultimately, consistent fillet weld quality depends on preparation, proper settings, and maintaining control of the weld pool. Whenever possible, positioning the work for easier access can improve both efficiency and weld quality.
The fillet positions are really a scale of how much help gravity gives you. In 1F it works with you, in 2F it starts to pull on the top leg, and by 3F and 4F it is working against the puddle the entire time. Knowing what each code asks for lets you set your angles, heat, and travel speed before the arc is lit instead of chasing the bead after it. What does not change from one position to the next is the fit-up. A joint that is square, tight, and held steady gives you the same target every time, whether it is sitting flat on the table or hanging overhead. H&K Fabrication makes tools for welders who want that kind of consistency, including roll out wheels, jack stands and heads, and pipe fitting squares built for real shop and field work. Take a look through our catalog today!
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