For some geometric tolerances that are applied to a feature of size, you must specify a material condition modifier (MMC, LMC, or RFS per Rule #2) for the tolerance zone. Keep in mind that the MMC and LMC modifiers introduce a bonus tolerance to the specified tolerance zone.

The function of the workpiece is the primary factor for material requirement selection. The table below provides a guide for deciding where MMC, LMC, or RFS should be indicated. One of the most common functions for the workpiece is assembly (e.g., the feature of size is assembled to another feature of size); therefore, MMC is the most common tolerance zone material requirement.