Welding Reference
A shop-floor guide to reading weld symbols, naming joints and picking a filler metal and process. Designers use it to draw the right symbol; welders, inspectors and buyers use it to read one and choose the rod or wire. To size a weld, use the Weld Strength calculator.
What the page covers
- Weld Symbol Basics: a sketch of the reference line and arrow, and the shape of each basic weld symbol (fillet, groove types, plug/slot, spot and seam), per AWS A2.4 [1].
- Common Weld Joint Types: butt, lap, T, corner and edge joints, with the welds each usually takes.
- Filler Metal Selection: a picker. Choose the base metal (carbon steel, aluminum, 304 or 316 stainless) and the process, and it lists the usual fillers with their AWS A5 specification [2], practical notes from the makers’ catalogs [3] and the shielding.
- Welding Process Comparison: SMAW, GMAW, GTAW and FCAW by typical use, portability, cost and shielding.
Reading symbols and filler names
The arrow points to the joint. A symbol below the reference line means weld the arrow side, above means the other side, and on both means both sides. A tail holds the process or spec.
A stick electrode name such as E7018 reads: E for electrode, 70 for 70,000 psi minimum tensile strength, 1 for all positions, and the last two digits together for the coating and current. An ER prefix marks a bare wire or rod that can be an electrode or a filler rod, and an L suffix on stainless means low carbon.
Limits and common mistakes
- The picker is a selection guide. The welding procedure specification and the governing code set the filler for a job.
- Don’t swap the sides. Below the line is the arrow side, whichever way the arrow points.
- Low-hydrogen rods such as E7018 pick up moisture. Store them dry, or they can cause hydrogen cracking.
- Stainless to carbon steel is a dissimilar joint and takes an over-alloyed filler such as ER309L, not ER308L.
Worked example
A mild-steel bracket is to be fillet-welded to a column flange on site, on the near side only. You need the symbol for the drawing and the rod for the welder.
- In Common Weld Joint Types, the T-joint row gives “Fillet (or partial/full-penetration groove for heavy loads)”. A fillet suits a bracket.
- In Weld Symbol Basics, draw the fillet triangle below the reference line, with its upright leg on the left, so the weld goes on the arrow side.
- Under Filler Metal Selection, choose Base metal Carbon / mild steel and Welding process SMAW (Stick), for outdoor work. The picker lists:
E7018 · AWS A5.1
E6010 · AWS A5.1
E6011 · AWS A5.1
Shielding: Flux coating decomposes to shield the arc
Take E7018, which the picker notes is “Standard for code-quality structural steel”. Check the strength: E70 means 70 ksi minimum tensile, above the 58–80 ksi of A36 steel, so the weld overmatches the plate. Then size the leg in the Weld Strength calculator.
Weld Symbol Basics
Reference line = the horizontal line; arrow = points to the joint; symbol below the line = weld on the arrow side (as shown here, a fillet weld).
| Weld Type | Symbol Shape |
|---|---|
| Fillet | Right triangle sitting on the reference line; the perpendicular leg is always drawn on the left, regardless of arrow direction |
| Square groove | Two short parallel lines, perpendicular to the reference line, open at the ends |
| V-groove | A "V" open away from the reference line; both members symmetrically beveled (a double-V forms an X/hourglass shape) |
| Bevel groove | One straight vertical line (square edge) + one angled line, forming a half-V; only one member is beveled, arrow points to it |
| U-groove | A "U" (curved bottom) open away from the reference line; both members have a radiused (J-shaped) edge prep |
| J-groove | A "J" shape — one square (vertical) side + one radiused side; only one member is prepped |
| Plug/Slot | Rectangle sitting on the reference line (weld fills a round hole = plug, elongated hole = slot) |
| Spot | Plain circle, typically straddling the reference line |
| Seam | A circle with two parallel lines through it, extending past the circle on both sides |
Common Weld Joint Types
| Joint Type | Typical Weld Type | Notes |
|---|---|---|
| Butt joint | Groove (square, V, bevel, U, J) | Two pieces in the same plane; full-penetration groove welds give maximum strength — standard for plate/pipe structural or pressure work |
| Lap joint | Fillet (also plug/slot) | Two pieces overlapped; easy fit-up, no edge prep, but stress concentration at the overlap — common on sheet metal |
| T-joint | Fillet (or partial/full-penetration groove for heavy loads) | One member perpendicular to another; extremely common in structural framing |
| Corner joint | Fillet (open corner) or groove (closed/flush corner) | Two edges meeting at ~90°; common in sheet-metal boxes/frames/enclosures |
| Edge joint | Edge weld (surface/flange weld along adjoining edges) | Weakest joint type — not for load-bearing work; used for sealing thin sheet edges |
See the Weld Strength calculator to size a fillet weld's throat and check shear stress against an applied load.
Filler Metal Selection
Welding Process Comparison
| Process | Typical Use | Portability/Cost | Shielding |
|---|---|---|---|
| SMAW (Stick) | Field repair, structural/maintenance, outdoor/windy or dirty conditions | Highest portability, lowest cost (no gas, no wire feeder) | Flux coating decomposes to shield the arc |
| GMAW (MIG) | Production/shop fabrication, thin-to-medium sheet & plate, automotive | Moderate cost; needs gas cylinder + wire feeder | External shielding gas (Ar/CO2 blends or straight CO2) |
| GTAW (TIG) | Precision work, thin material, aluminum/stainless/exotic alloys, pipe root passes | Higher cost, least portable, typically shop-based | Inert gas, typically pure Argon |
| FCAW (Flux-core) | Heavy structural steel, thick material, outdoor/high-deposition production | Moderate cost; self-shielded variant is portable and wind-tolerant | Self-shielded or gas-shielded variant |