Least material condition (LMC) is the permitted size containing the least material: the largest hole or the smallest pin. A circled L after an eligible geometric tolerance lets that allowance grow as the feature gains material, while preserving a boundary that protects remaining stock.
Datum required
Depends on the geometric control; position uses A and B here
MMC / LMC applicable
LMC on an eligible feature of size
Control type
Material-condition modifier
What it controls
Size-dependent geometry and a least-material boundary
Typical features
Holes near edges; features protecting minimum stock
01 / PURPOSE
Why is this annotation used?
LMC is useful when keeping enough material matters more than preserving assembly clearance. Examples include a bore near an edge, a thin wall or a feature with a required machining allowance.
A smaller hole or larger pin leaves more material. LMC converts that size departure into additional geometric tolerance while maintaining a defined material-protection boundary. Manufacturing gets more freedom without sacrificing the minimum stock requirement. Size limits still apply.
Inspection evaluates size, geometry and datums together. A simple MMC clearance gauge does not prove LMC compliance; assess the specified least-material boundary and actual geometry.
02 / APPLICATION
Which controls permit LMC?
Under ASME Y14.5, apply LMC only to an eligible feature of size when preserving remaining material is important:
⌖Position: holes, pins, slots and tabs with a material-protection boundary.
⊥ ∥ ∠Perpendicularity, parallelism and angularity: axis or centre-plane orientation of a feature of size; not a single surface.
—Straightness: the derived median line or plane of a feature of size; not a surface line.
▱Flatness: the derived median plane of a width-type feature of size; not surface flatness.
INTERACTIVE APPLICATION
The same hole, with and without LMC
Hole Ø10 ±0.1 mm · Position Ø0.20 at LMC · Primary right face A, secondary front face B. All dimensions are in mm.
Green: actual holeOrange: actual axisPurple: position zone
Start at the largest hole: LMC = Ø10.10
Both callouts permit Ø0.20 position at this size. The maximum radial axis displacement is 0.10 mm. The limiting hole boundary is Ø10.30, leaving 8 − 10.30 / 2 = 2.85 mm to face A. With LMC, that boundary stays fixed as the hole becomes smaller; without LMC, the position allowance stays fixed.
Without LMCFixed position allowance (RFS)
At actual hole diameter Ø10.10 mm
Hole sizeØ10.10Permitted positionØ0.20Limiting boundaryØ10.30Minimum wall2.85 mm
With LMCMaterial-protection boundary
At actual hole diameter Ø10.10 mm
Hole sizeØ10.10Permitted positionØ0.20Limiting boundaryØ10.30Minimum wall2.85 mm
A smaller hole leaves room for more position tolerance
At Ø9.90, without LMC the Ø0.20 position allowance remains unchanged: the limiting hole boundary becomes Ø10.10 and the minimum wall becomes 2.95 mm. With LMC, 0.20 mm bonus permits Ø0.40 position while retaining the Ø10.30 boundary and 2.85 mm minimum wall.
Without LMCFixed position allowance (RFS)
At actual hole diameter Ø9.90 mm
Hole sizeØ9.90Permitted positionØ0.20Limiting boundaryØ10.10Minimum wall2.95 mm
With LMCMaterial-protection boundary
At actual hole diameter Ø9.90 mm
Hole sizeØ9.90Permitted positionØ0.40Limiting boundaryØ10.30Minimum wall2.85 mm
Practical benefit: accept more axis-location variation when the smaller hole leaves enough material. The permitted Ø9.90–10.10 size range does not change. The plan views illustrate each permitted limit towards face A; a real hole need not use the whole allowance.
03 / DRAWING
Apply LMC to protect the remaining wall
Drawing callout
This example uses position at LMC to protect the wall between a hole and the right-hand datum face A.
Steps to add it to a drawing
Identify the wall or stock boundary that must be protected.
Set hole size limits Ø9.90–10.10 and basic distances 8.
Specify position Ø0.20 Ⓛ to primary A and secondary B.
Verify the least-material boundary and account for the outer edge’s own tolerances.
How to read it
Ⓛ after Ø0.20 means that allowance applies at the largest hole, Ø10.10. At Ø9.90, bonus is 10.10 − 9.90 = 0.20 and total position is Ø0.40. The least-material virtual-condition boundary remains Ø10.30.
For a hole or internal feature, LMC is the largest permitted size.
For a pin or external feature, LMC is the smallest permitted size.
Why A and B?
A is the right face and B is the perpendicular front face. The true centre is defined as 8 mm from each face (basic). Together, these planes locate and orient the through-hole axis parallel to their intersection. Translation along that axis does not affect this position requirement, so no third datum is needed. Both planar faces are referenced without material-boundary modifiers.
Protected wall: 8 − 10.30 / 2 = 2.85 mm to A in the idealised example. The bonus comes from a smaller hole, not from relaxing its size limits.
APPLY THE EXAMPLE
LMC position tolerance calculator
For a cylindrical hole or shaft with position specified at LMC. All position tolerances are diametrical. Actual size must remain inside its size limits.
LMC diameter
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Bonus tolerance (diametrical)
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Total position tolerance (diametrical)
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Least-material virtual-condition diameter
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Calculation steps
For a hole: protected boundary = LMC + position tolerance at LMC.
ASME Y14.5-2018 (R2024)
This page uses ASME Y14.5 terminology and datum precedence. The worked position example protects a least-material boundary; use the edition specified on the drawing when determining eligibility and acceptance.
