Which dimension convention should be used?

• A. Arbitrary dimensions
• B. Nominal dimensions
• C. Calculated dimensions
• D. Toleranced dimensions

Answer: (B)

Dimension conventions establish the reference size that a part is designed and inspected to. The intended target size is expressed as a nominal dimension, and tolerances describe how much the actual part may deviate from that target. This keeps a clear baseline for manufacturing and quality control: the part is made to the nominal size, and any variation must fall within the specified tolerance.

Arbitrary dimensions lack a standardized target, making it unclear what the part should truly measure. Calculated dimensions are derived from relationships or other features and aren’t used as the base reference for the part’s size. Toleranced dimensions convey allowable variation around a nominal size but don’t specify the target size by themselves. Therefore, using nominal dimensions as the convention is the correct approach.