Fillet weldA weld of triangular cross-section joining two surfaces at an angle. Here in a T joint.
FaceThe outer surface of the weld, the side you see. It can be flat, concave or convex.
RootThe deepest point of the weld, in the corner opposite the face.
Base metalThe metal pieces being joined, also called the parent metal.
The fillet weld: 7 4
ToesThe two edges where the face of the weld meets the plates.
LegsThe two sides of the weld along the plates. The leg length is usually given as the weld's size.
ThroatThe distance from the root to the middle of the face. It is usually at least as thick as the metal being welded.
Heat-affected zoneMetal next to the weld that did not melt. It was changed by the heat of welding.
The groove weld: 7 5
Groove weldWeld metal filling the groove between two plates of a butt joint.
ReinforcementWeld metal that stands above the surface of the plates. It is not counted in the weld's thickness.
BevelThe angled edge cut on a plate to make the groove. In a V groove both edges are bevelled.
Groove angleThe whole angle between the two bevels. It is kept as small as still gives the welder access.
Root openingThe gap between the plates at the joint's root.
How this list was compiled: Read 2026-09-27. (1) Wikipedia, Fillet weld, https://en.wikipedia.org/wiki/Fillet_weld : five parts, the root (the deepest penetration, opposite the hypotenuse), the toes (the edges of the hypotenuse), the face (the outer visible side, concave, flat or convex), the legs (the other two sides; the leg length is usually the size of the weld) and the throat (from the centre of the face to the root, usually at least as thick as the metal welded). (2) Wikipedia, Welding joint, https://en.wikipedia.org/wiki/Welding_joint : butt joints and grooves; single-V welds have both edges bevelled; the opening or gap at the root and the included angle of the groove are chosen to need the least weld metal that still gives access; a butt weld's thickness does not count the weld reinforcement; base metals. (3) Wikipedia, Heat-affected zone, https://en.wikipedia.org/wiki/Heat-affected_zone : base material that is not melted but has had its properties altered by the heat of welding. Licence: own work
The drawing: Drawn for this site by script, 2026-09-27. Own work, nothing traced. Licence: own work
How it works
To label the parts of a weld, write a name on the line for each number. Numbers 1 to 7 are on a fillet weld in a T joint. Numbers 8 to 13 are on a V-groove butt weld underneath.
Read the full guide
Word bank: 7 names on the fillet weld, then the groove weld
Numbers 1 to 7, in alphabetical order: face, fillet weld, heat-affected zone, legs, root, throat, toes. Numbers 8 to 13: base metal, bevel, groove angle, groove weld, reinforcement, root opening.
Labeling a fillet weld: the numbers that get swapped
Three dots sit on the corners of the triangle. Line 3 ends on the upper one; it and the dot at the other end of the sloping side are the toes. The dot in the inside corner is the root. Of the arrows, the two outside the plates are the legs, and the one inside the weld is the throat.
On the groove weld, the bevel is one slanted plate edge; the groove angle is the arc over both.
When marking, also accept HAZ on line 7, butt weld on line 9, included angle on line 12 and root gap on line 13.
Questions and answers
What is a weld bead?
The line of weld left as a puddle of molten metal is pushed along a joint (source: Wikipedia, Welding). Each weld here is drawn as one bead seen end on, so labeling a weld bead uses the same names, from face and toes to root.
What is the difference between a concave and a convex fillet weld?
The shape of the face. It curves inward on a concave weld, bulges outward on a convex one, and is straight on a flat one, as drawn here. The welder's technique sets it, or grinding after the weld is finished.
What is a T joint in welding?
Two pieces joined at a right angle in the shape of a T, as the upright plate and the flat plate are on this sheet. Butt, corner, edge and lap joints are the other basic types.
What is the difference between a single-V and a double-V weld?
A single-V joint, as drawn here, has both plate edges beveled to make one V. A double-V joint has a V on each side of the plates. It is used on thick metal that can be welded from both sides, and takes less filler.