Drafting best practice: There should be a small, visible gap between the object (for example, a wall edge) and which line used to project dimensions?

Introduction / Context:
Good linework prevents visual confusion. One common rule is to keep extension lines slightly offset from the object so the reader can distinguish object edges from dimension indicators.

Given Data / Assumptions:

• The feature is a wall or object edge in a plan or elevation.
• We must name the line that should not touch the object.
• We assume conventional dimensioning standards.

Concept / Approach:

Extension lines originate near the object but begin with a small gap (often around 1–2 mm on paper scale). This visual break avoids merging with the object line and keeps the drawing clean. Dimension lines span between extension lines and carry the value.

Step-by-Step Solution:

Verification / Alternative check:

Graphic standards handbooks illustrate this gap to improve clarity and prevent misinterpretation of where the feature ends versus where dimensioning begins.

Why Other Options Are Wrong:

Dimension: sits between extensions; not the line adjacent to the object.

Center: marks axes and symmetry; unrelated to object-to-line gaps.

Leader: angled note indicator; not used for baseline dimensioning.

Common Pitfalls:

Letting extension lines touch or cross object lines excessively, which clutters drawings and confuses readers.

Final Answer:

extension