What is a secondary datum feature?

• A. A reference feature that serves as the primary datum
• B. A feature used solely for aesthetic purposes
• C. A reference feature used to assist primary datum controls
• D. A non-physical reference point in the design

Answer: (C)

A secondary datum feature is a reference feature that helps to establish the position and orientation of other features on a part, supplementing the primary datum. This means that after the primary datum has been established, the secondary datum provides additional points or planes against which other elements of the part can be measured or aligned.

By having a secondary datum, it enhances the overall accuracy and reliability of the measurements taken from the primary datum. This is particularly important in complex assemblies where multiple features must fit together correctly, as it ensures that there is not just one point of reference, but also a related reference that supports the primary one.

The other options do not accurately define the concept of a secondary datum feature. For example, referring to a primary datum or a non-physical reference point does not capture the essence of what a secondary datum does in terms of measurement and positional control. Additionally, a feature solely for aesthetic purposes does not contribute to the functional aspects of positioning and aligning parts in manufacturing or assembly.