Weld symbol
Spot weld symbol
A circle on the reference line calls for spot welds: individual fused nuggets made between overlapping sheets, dimensioned by nugget diameter or strength, how many, and how far apart.
Reads asArrow side: spot weld, 1/4 size, 2 pitch, 8 welds.
How to read it
The spot weld symbol is a plain circle. It describes a weld made by squeezing two overlapping sheets between electrodes and passing current through them until a lens of metal fuses at the interface. Nothing is added - no filler, no groove - so the symbol carries no size in the groove sense and instead reports the nugget that forms between the sheets.
The number to the left of the circle is normally the nugget diameter at the faying surface, the plane where the two sheets touch. Some drawings substitute a required strength per spot instead of a diameter, in which case the units make it obvious. Either way the number describes the result of the weld, not a dimension the operator sets directly, since nugget size comes from current, time, and force.
A count in parentheses gives how many spots the callout covers and a pitch to the right gives the centre-to-centre spacing along the joint. Where the spots are not evenly spaced or follow a pattern that a single pitch cannot capture, the drawing locates them and the symbol simply says what each one is.
Because the weld forms between the sheets rather than on a visible face, a spot weld symbol may be drawn centred on the reference line rather than clearly above or below it when the process itself decides which side the electrodes reach from. When it is drawn on one side, read that as the arrow side in the usual way, and check the drawing for electrode access before assuming either.
Where each dimension goes
- Nugget diameter (left of the circle)
- Diameter of the fused lens at the plane where the two sheets touch.
- Strength per spot
- An alternative to diameter on some drawings, giving the load each spot must carry rather than its size.
- Count (in parentheses)
- How many spot welds the callout covers.
- Pitch (right of the circle)
- Centre-to-centre spacing between adjacent spots along the joint.
Worked examples
Each one is a drawing, the sentence it comes out as, and then the mark-by-mark account of why. Read the sheet first and say the sentence yourself before you look down.
Example 1: Evenly spaced spots on a lap seam
TitleEvenly spaced spots on a lap seamRefSpot weldEx1 / 2Reads as
Make twelve spot welds with 1/4 nuggets on two-inch centres along the lap.
Which mark says so
- spot symbolBelow the reference lineA spot weld on the arrow side of the joint
- 1/4Left of the symbolSize of each weld - diameter for a spot, width for a seam
- -2Right of the length on the symbolPitch - centre to centre spacing of an intermittent weld
- (12)In parentheses beside the symbolHow many welds are called for
The 1/4 left of the circle is the nugget diameter at the faying surface, the parenthesised 12 is the count, and the 2 to the right is the centre-to-centre spacing.
And what it does not say
- No length is given, so each weld runs the full length of the joint.
- Nothing sits above the reference line, so the far face of the joint stays bare.
- There is no circle at the elbow, so the weld does not continue around the joint.
Example 2: Spot welds specified by strength
TitleSpot welds specified by strengthRefSpot weldEx2 / 2Reads as
Make six spot welds, each developing at least 800 pounds of shear.
Which mark says so
- spot symbolBelow the reference lineA spot weld on the arrow side of the joint
- 800 lbLeft of the symbolSize of each weld - diameter for a spot, width for a seam
- -1-1/2Right of the length on the symbolPitch - centre to centre spacing of an intermittent weld
- (6)In parentheses beside the symbolHow many welds are called for
Where a strength value replaces the diameter to the left of the circle, the drawing is controlling the result rather than the nugget size, and the units make the substitution obvious.
And what it does not say
- No length is given, so each weld runs the full length of the joint.
- Nothing sits above the reference line, so the far face of the joint stays bare.
- There is no circle at the elbow, so the weld does not continue around the joint.
Common mistakes
- Reading the number left of the circle as an electrode tip diameter rather than a nugget diameter.
- Measuring the nugget at the sheet surface instead of at the faying interface.
- Ignoring the count and putting down as many spots as look right along the seam.
- Assuming a spot weld symbol drawn on the reference line centre means both sides get welded.