For a feature of size such as a hole or shaft, its actual size can affect how much geometric variation is acceptable while the assembly still functions.

GD&T expresses this interaction using material condition modifiers.

Maximum material condition

Maximum material condition (MMC) is the size at which the feature contains the greatest amount of material: the smallest permitted hole or largest permitted shaft.

A geometric tolerance specified at MMC can gain bonus tolerance as the actual feature departs from MMC, because additional clearance becomes available.

Least material condition

Least material condition (LMC) is the opposite size extreme: the largest hole or smallest shaft.

It is useful when minimum wall thickness or edge distance must be protected.

Regardless of feature size

With regardless of feature size (RFS), the stated geometric tolerance does not change with the actual feature size.

Functional gauges

MMC-based controls can often be interpreted through a virtual boundary that a mating feature must not violate. This allows assembly function to be checked with simple functional gauges rather than by independently judging every dimensional and geometric error.