AWS A2.4 weld symbol
Slot Weld Symbol
A slot weld symbol is the same rectangle as a plug weld, but it calls for an elongated slot rather than a round hole, giving more weld area per opening.
How to read the slot weld symbol
- The slot weld uses the same rectangular symbol as the plug weld; the dimensions and a detail view distinguish them.
- The slot width is given to the left of the symbol and the length to the right.
- Depth of filling goes inside the rectangle; omitted means filled flush.
- The number of slot welds appears in parentheses.
- Slot orientation cannot be shown on the symbol alone — it must be given on a detail on the drawing.
Where the dimensions go
| Position | What it specifies |
|---|---|
| Left of the symbol | Width of the slot |
| Right of the symbol | Length and pitch |
| Inside the symbol | Depth of filling; omitted means flush |
| In parentheses | Number of slot welds |
Joint types
- Lap joint
- T-joint
Practical notes
- A slot gives more fusion area than a plug of the same width, so fewer openings are needed for the same joint strength.
- Slot orientation and location always require a detail view; the welding symbol cannot convey them.
- As with plug welds, the slot must be cut before welding.
Slot Weld symbol — common questions
What does a slot weld symbol look like?
A rectangle on the reference line — identical in shape to the plug weld symbol. The width, length and the drawing's detail view are what identify it as a slot.
How is slot orientation specified?
Not on the symbol. AWS A2.4 requires the orientation to be shown on a detail on the drawing, because the welding symbol has no way to express it.
Why use a slot weld instead of a plug weld?
A slot provides more fused area per opening, so a joint can reach the required strength with fewer openings and less drilling.
Does the slot need to be filled completely?
Unless a depth of filling is written inside the rectangle, yes — the slot is filled flush with the surface of the upper member.
Welding symbol anatomy
Every weld symbol attaches to the same framework. If any part of the diagram above is unfamiliar, the full guide to reading welding symbols walks through the whole system.
| Reference line | The horizontal backbone of every welding symbol. Everything else attaches to it, and it is always drawn horizontal on the drawing. |
|---|---|
| Arrow | The leader and arrowhead that connect the reference line to the joint. The side of the joint the arrow touches is the arrow side. |
| Weld symbol | The shape that says which kind of weld is required — triangle for a fillet, V for a V-groove, circle for a spot, and so on. |
| Arrow side (below the line) | A weld symbol drawn below the reference line calls for a weld on the side of the joint the arrow points to. This is the convention that catches people out most often. |
| Other side (above the line) | A weld symbol drawn above the reference line calls for a weld on the far side of the joint. |
| Both sides | Symbols drawn above and below the reference line call for welds on both sides of the joint. |
| Tail | An optional fork at the far end of the reference line, used to reference a specification, process or procedure such as GMAW or a WPS number. |
| Dimensions | Size is placed to the left of the weld symbol; length and pitch are placed to the right. |