Back or backing weld
A filled half circle on the reference line: a back or backing weld, a bead deposited at the back of a single groove weld.
This explains what a symbol specifies on a drawing. It isn't welding instruction, and a drawing's own notes and the governing code take precedence.
How to read it
A back weld is deposited at the back of a single groove weld, and a backing weld is backing in the form of a weld. The symbol is placed on the side of the reference line opposite the groove weld symbol it goes with. Dimensions of back or backing welds are not shown on the welding symbol.
Differences by country or standard
India's IS 813:1986, which draws on ISO 2553, lists the same weld as a backing run, back or backing weld.
More welding symbols
Sources
- Welding Theory and Application, TM 9-237, 1967, Department of the Army (Internet Archive), Chapter 11, section II; glossary
- Scheme of symbols for welding, IS 813:1986, Bureau of Indian Standards (Internet Archive, Public.Resource.Org), Table 1
Last reviewed September 25, 2026 by Rory Hansen. How we research