Joint root

From GAWDAwiki

Joint root is the part of a joint that comes closest together where the weld is to be made. This may be an area of the joint or just a line or point of that joint.^[1]

The size of the root opening determines how much weld metal is needed to obtain fusion at the root.^[2]

References

1. http://www.millerwelds.com/interests/instructors/pdf/Glossary.pdf
2. http://www.toolingu.com/definition-650130-77160-root-opening.html