How is perpendicularity different from parallelism?

How is perpendicularity different from parallelism?

• A. Perpendicularity controls the angle between a feature and a datum plane; Parallelism controls a feature’s local drift along a direction relative to a datum.
• B. Perpendicularity controls the maximum material condition; Parallelism controls the least material condition.
• C. Perpendicularity controls the thickness; Parallelism controls the width.
• D. Perpendicularity and Parallelism are the same and interchangeable.

Answer: (A)

Perpendicularity is about keeping a feature at a right angle to a reference datum; it restricts how far the feature’s orientation can deviate from 90 degrees to that datum. Parallelism is about maintaining the feature so that it runs in the same direction as a reference datum, meaning it stays parallel rather than tilting toward or away from the datum. In GD&T, the perpendicularity tolerance uses planes perpendicular to the datum to bound the feature’s angular error, while the parallelism tolerance uses planes parallel to the datum to bound how much the feature can drift in orientation along its length. Use perpendicularity when you need a true 90-degree relationship, and use parallelism when you need the feature to stay oriented parallel to the datum. The other options mix in material conditions or dimensions and aren’t what these controls address.

Perpendicularity is about keeping a feature at a right angle to a reference datum; it restricts how far the feature’s orientation can deviate from 90 degrees to that datum. Parallelism is about maintaining the feature so that it runs in the same direction as a reference datum, meaning it stays parallel rather than tilting toward or away from the datum. In GD&T, the perpendicularity tolerance uses planes perpendicular to the datum to bound the feature’s angular error, while the parallelism tolerance uses planes parallel to the datum to bound how much the feature can drift in orientation along its length. Use perpendicularity when you need a true 90-degree relationship, and use parallelism when you need the feature to stay oriented parallel to the datum. The other options mix in material conditions or dimensions and aren’t what these controls address.