What is the MMC of an internal feature?

• A. Higher limit of the dimension
• B. Mean value of the dimension
• C. Upper limit of the dimension
• D. Lower limit of the dimension

Answer: (D)

The Maximum Material Condition (MMC) for an internal feature refers to the condition where the feature contains the maximum amount of material while still being within specified limits. For internal features, such as holes, the MMC is defined at the smallest size of the opening, which corresponds to the lower limit of the dimension.

This concept is crucial in the context of fit and assembly, as it allows for tighter control of conditions that can affect the assembly of parts. When a hole is at its MMC, it restricts the maximum size of the shaft that can fit into it, ensuring that parts will assemble correctly while allowing for variation in manufacturing.

Understanding MMC is essential in applying GD&T effectively, as it helps in determining acceptable limits and relationships between mating parts. In the case of an internal feature, the smallest permissible size ensures that the parts will not impose excessive forces or misalignments during assembly.