AWS A2.4 weld symbol
Plug Weld Symbol
A plug weld symbol is a rectangle on the reference line, calling for a round hole in one member to be filled with weld metal so it fuses to the member beneath.
How to read the plug weld symbol
- The rectangle is drawn on the arrow side or other side to say which member is drilled — the hole goes in the member the arrow touches when the symbol is below the line.
- The hole diameter is written to the left of the symbol.
- Depth of filling is written inside the rectangle. If it is omitted, the hole is filled flush.
- The angle of countersink, if any, is written above or below the symbol.
- The number of plug welds in parentheses and the pitch to the right of the symbol.
Where the dimensions go
| Position | What it specifies |
|---|---|
| Left of the symbol | Hole diameter |
| Inside the symbol | Depth of filling; omitted means filled flush |
| Above or below the symbol | Angle of countersink |
| Right of the symbol | Pitch, with the number of welds in parentheses |
Joint types
- Lap joint
- T-joint
Practical notes
- Plug welds replace rivets and mechanical fasteners on lap joints, and are common in automotive body work.
- A plug weld symbol may not be used on both sides of the reference line for the same joint.
- The hole must be prepared in advance — burning through with the arc is not a plug weld and will not be accepted on code work.
Plug Weld symbol — common questions
What is the difference between a plug weld and a slot weld?
The hole shape. A plug weld fills a round hole; a slot weld fills an elongated one. Both use the same rectangular symbol — the dimensions and the drawing detail tell them apart.
What does the number inside the plug weld rectangle mean?
The depth of filling. If nothing is shown, the hole is to be filled flush with the surface of the upper member.
Which member gets the hole?
The one the arrow touches, when the symbol is drawn below the reference line. A symbol above the line puts the hole in the far member.
Are plug welds the same as spot welds?
No. A plug weld fills a pre-drilled hole with deposited filler metal by arc welding. A spot weld fuses two sheets at their interface with resistance heating and needs no hole.
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. |