Weld symbol
V-groove weld symbol
A V drawn on the reference line calls for a V-groove weld. Both members are bevelled, and the symbol carries three numbers: the included angle, the root opening, and the depth of the groove.
Reads as: Arrow side: V-groove weld, 1/2 size, 60° groove angle, 1/8 root opening.
How to read it
The V shape says both members are prepared. Each edge is cut back at an angle so that together they form a vee opening toward the face being welded. That symmetry is the difference between a V-groove and a bevel groove, where only one member is cut, and it is the reason a V-groove symbol needs no broken arrow to say which member gets prepared.
Three numbers do the work. The included angle sits beyond the open end of the V and is the total angle between the two prepared faces, not the angle of one face off vertical. The root opening sits inside the V and is the gap between the two root faces at the bottom. The size sits to the left, giving how deep the groove is filled with weld metal.
Angle and root opening trade against each other. A wider included angle gives the electrode more room to reach the root but adds weld metal, cost, and shrinkage. A larger root opening lets a narrower angle still reach the root. Reading the pair together tells you a lot about the intent: a tight angle with a generous gap usually means an open root pass, while a wide angle with a closed root suggests a backing or a back weld is coming.
A V above the line as well as below means both faces of the joint are prepared and welded, which is a double-V. A V below the line with a semicircle above it means the joint is welded from the front and then dressed and welded from the back. Reading the whole reference line before starting is the only way to know which of those you are looking at.
Where each dimension goes
- Included angle (beyond the V)
- Total angle between the two prepared faces, measured across the joint, not the angle of a single face.
- Root opening (inside the V)
- Gap between the two root faces at the bottom of the groove before welding.
- Groove weld size (left of the symbol)
- Depth of the joint filled with weld metal, which on a full-depth joint equals the material thickness.
- Effective throat (in parentheses)
- Where preparation depth and effective weld throat differ, the throat is written in parentheses after the depth.
Worked examples
Open-root V-groove on pipe
“Prepare a 60 degree included angle with a 1/8 root gap and fill the groove 3/8 deep.”
The 60 degrees beyond the V is the total angle across both prepared faces, the 1/8 inside the V is the root gap, and the 3/8 left of the symbol is how deep the weld metal goes.
V-groove with depth and effective throat called out separately
“Cut a 45 degree vee 1/2 deep and expect a 3/8 effective throat from the weld.”
Two numbers appear left of the symbol: the preparation depth first, then the effective throat in parentheses. They differ because the weld is not carried the full depth of the preparation.
V-groove backed by a weld on the far side
“Weld the arrow-side vee, then back gouge and lay a back weld on the far side.”
The V below the line is the main groove and the semicircle above it is the back weld deposited after the root is cleaned out from the opposite face.
Common mistakes
- Reading the included angle as the bevel angle of one member, which halves the preparation.
- Confusing the root opening inside the V with the groove weld size to the left of it.
- Missing a semicircle above the reference line and skipping the back weld entirely.
- Assuming every V-groove is a full-depth weld when a size to the left says otherwise.
Typical joints
Related symbols
Practise reading welds, not just symbols
The drawing tells you what the weld should be. The gauge trainer is where you find out whether you can tell what it actually is.