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Foundation 04

Least Material Condition (LMC)

A material-condition modifier used when the least amount of material is the functionally critical condition.

Least material condition, written with a circled L, is the size condition where a feature contains the least material. For a hole, that is its largest permitted size. For a shaft or pin, it is its smallest permitted size.

When LMC makes sense

LMC is useful when minimum remaining material matters. Examples include preserving wall thickness around a hole, keeping enough edge distance, or maintaining strength in a thin feature.

How the tolerance changes

When LMC modifies a geometric tolerance on a feature of size, the stated tolerance applies at LMC. As the actual feature size moves away from LMC toward more material, the feature can gain bonus geometric tolerance.

A less common—but important—tool

MMC is encountered more often in assembly-fit callouts, but LMC is valuable when the design risk is breaking through a wall or leaving too little material. Use it when that condition is truly functional, not simply because it is available.

Example: protecting a thin wall

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A hole near an outside wall may use LMC so its position is tightest when the hole is largest—the condition that leaves the least wall material.

Common mix-up

LMC is about the least-material size of the controlled feature. It is not a general instruction to make the part lighter or thinner.

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