Engineering Reference

MMC / LMC (maximum and least material condition)

The size limits at which a feature has the most or least material.

Definition

For a hole, MMC is the smallest permissible diameter and LMC the largest. For a shaft it is the reverse. The distinction matters because it determines the virtual condition and therefore the bonus tolerance available.

Specifying a positional tolerance at MMC lets a hole that is made oversize gain extra position tolerance — the departure from MMC is added to the tolerance. It is a real manufacturing saving on clearance holes.

Common misuse

Applying the MMC modifier where the joint does not have clearance. If a pin must fit a hole exactly, bonus tolerance is not permissible.

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