Engineering drawing — purpose of centerlines Center lines are used to locate or represent the centers of which features on a technical drawing?

Introduction / Context:
Centerlines are one of the most frequently used line types in mechanical and architectural drafting. Understanding what they represent ensures that geometry is interpreted correctly for manufacturing, inspection, and construction. This question tests recognition of where centerlines apply on drawings.

Given Data / Assumptions:

• A standard centerline is drawn as alternating long and short dashes with a thin line weight.
• Drawings may show both visible and hidden round features.
• We assume conventional standards such as ASME Y14 or ISO line conventions.

Concept / Approach:
Centerlines indicate symmetry and the exact geometric center of circular or arc features. They are also used to show axes of cylinders, bolt circles, and any radial pattern. Whether a feature is visible in the view or hidden behind other geometry, its center can still be indicated by a centerline or center mark to guide dimensioning and machining setups.

Step-by-Step Solution:

Verification / Alternative check:
Open any standard drawing standard (e.g., ASME Y14 series). You will find centerlines defined for circles, arcs, and axes of symmetry. Hidden status of the geometry does not change the centerline's purpose; the line type for the centerline remains the same while the geometry edges may be drawn hidden.

Why Other Options Are Wrong:

• Arcs only / circles only: too narrow; centerlines are used more broadly.
• Hidden round features only: incomplete; visibility does not limit centerline use.
• Only visible holes, not hidden ones: incorrect; hidden features still require centers for dimensioning and layout.

Common Pitfalls:

• Confusing centerlines with hidden lines; centerlines use long–short–long pattern, while hidden lines use uniform short dashes.
• Omitting centerlines on symmetric features, which can cause ambiguity in hole locations and tolerancing.

Final Answer:
all of the above