Which statement best describes ISO 2553 System A reference lines?

Which statement best describes ISO 2553 System A reference lines?

• A. Two parallel lines, one solid and one dashed.
• B. Two parallel lines that are both solid.
• C. Two intersecting lines.
• D. A single line.

Answer: (A)

In ISO 2553 System A, the reference line for welding symbols is a pair of parallel lines, one solid and one dashed. This double-line baseline distinguishes System A and gives a clear, unambiguous origin for reading the rest of the weld symbol—the position, side, and orientation of the weld are determined relative to this paired reference. The dashed and solid lines together indicate this specific convention and help readers interpret the symbol consistently on international drawings. Other configurations (such as a single line or two solid lines) do not match System A’s standard, so the two parallel lines with one solid and one dashed best describe System A reference lines.

In ISO 2553 System A, the reference line for welding symbols is a pair of parallel lines, one solid and one dashed. This double-line baseline distinguishes System A and gives a clear, unambiguous origin for reading the rest of the weld symbol—the position, side, and orientation of the weld are determined relative to this paired reference. The dashed and solid lines together indicate this specific convention and help readers interpret the symbol consistently on international drawings. Other configurations (such as a single line or two solid lines) do not match System A’s standard, so the two parallel lines with one solid and one dashed best describe System A reference lines.