Least Material Condition

Least Material Condition (LMC) is a GD&T modifier defining the state of a feature when it contains the least amount of material allowed by its size limits. For an internal feature like a hole, LMC is the largest permitted hole; for an external feature like a pin or shaft, LMC is the smallest permitted diameter.

In a CNC cell, LMC is applied to protect minimum wall thickness or edge distance on features like bolt holes near thin flanges or slots cut close to edges. The part’s geometric tolerance is referenced to the least-material boundary, meaning that as the hole approaches its largest size, position tolerance tightens to ensure enough remaining material. Toolpath strategy must account for this: conservative stock allowance, rigid workholding, and controlled tool deflection are critical, especially on thin aluminum plates or cabinet hardware where breakout or tear-out can occur. Inspectors evaluate the combined effect of size and geometry at the worst-case material condition, not just diameter alone.