320 Quality Assurance
other feature that can be measured directly for size. On the other hand, the
irregular feature of size is new. It is dened as “a directly toleranced feature
or collection of features that may contain or be contained by an actual mat-
ing envelope.”
In addition to the above denitions, there are two rules of which the individ-
ual using GD&T must be aware. Rule #1 deals with perfect form at maximum
material condition (MMC). When a regular FoS is at its MMC, it cannot extend
beyond its boundary of perfect form at MMC. Rule #1 does not apply when
• FoS is not involved or when the FoS is irregular or if listed in “Other
exceptions to Rule #1”
• Stock sizes: materials produced to industry or government stan-
dards (e.g., 2×4s, ...