What does perpendicularity mean in GD&T?

• A. The tolerance that a feature must be parallel to a referenced datum.
• B. The tolerance that a feature must be at fixed angle to a datum.
• C. The tolerance that a feature must be coaxial with a datum.
• D. The tolerance that a feature must be perpendicular to a referenced datum.

Answer: (D)

Perpendicularity in GD&T is about ensuring a feature is oriented at a true right angle to a referenced datum within the specified tolerance. The datum provides the reference orientation, and the tolerance defines how much the feature’s axis (or surface) can deviate from exactly 90 degrees relative to that datum. This is why the correct idea is that the tolerance must constrain the feature to be perpendicular to the datum. Other ideas describe different relationships: parallelism would require 0 degrees to the datum, a fixed angle that isn’t 90 degrees would set a different orientation, and coaxiality concerns sharing the same axis rather than orientation to a datum.