Maximum material condition (MMC) is the size that leaves the most material in a feature of size: the smallest hole or the largest pin. A circled M after an eligible geometric tolerance links the requirement to that size limit.
Datum required
Depends on the geometric control
MMC / LMC applicable
Yes — this is the MMC modifier
Control type
Material-condition requirement
What it controls
Combined size and eligible geometric variation
Typical features
Clearance holes and pins
01 / PURPOSE
Why is this annotation used?
MMC gives an eligible feature more geometric tolerance as it departs from the size containing the most material, while preserving a defined functional boundary. A smaller pin or larger hole can use the extra space without sacrificing the intended assembly fit. Size limits still apply.
This can reduce unnecessary rework and scrap, and let manufacturing trade available size clearance for geometric variation. Inspection can check the combined boundary with a suitable functional gauge, alongside size checks, rather than reject a usable part solely for exceeding the tolerance stated at MMC.
02 / APPLICATION
Which controls permit MMC?
For an ASME Y14.5 drawing, the modifier belongs to an eligible feature of size. These are the usual permitted combinations:
⌖Position: eligible features of size, such as holes, pins, slots and tabs.
⊥ ∥ ∠Perpendicularity, parallelism and angularity: axis or centre-plane orientation of a feature of size; not orientation of a single surface.
—Straightness: the derived median line or median plane of a feature of size; not a surface line element.
▱Flatness: the derived median plane of a width-type feature of size; not surface flatness.
INTERACTIVE APPLICATION
The same pin, with and without MMC
Pin Ø12.0 ±0.1 mm · Perpendicularity Ø0.10 mm to mounting face A · Bore Ø12.20 mm. All dimensions are in mm.
Green: actual pinOrange: actual axisPurple: cylindrical axis zoneBlue: gaugeDashed charcoal: limiting envelope
Same pin size limits; two different callouts
Without MMC, Ø0.10 applies at every permitted pin size (RFS under ASME).
With the circled M after Ø0.10, that allowance applies at the largest pin, Ø12.10, and grows as the pin becomes smaller.
Without MMC Fixed geometric tolerance
Pin Ø12.10Permitted zone Ø0.10Envelope Ø12.20Diametrical clearance 0.00
With MMC Size-dependent allowance
Pin Ø12.10Permitted zone Ø0.10Envelope Ø12.20Diametrical clearance 0.00
At Ø11.90, MMC turns available clearance into tolerance
Without MMC: the fixed Ø0.10 axis zone gives a Ø12.00 limiting envelope: 0.20 mm diametrical clearance to the Ø12.20 bore, or 0.10 mm on each side of the centred envelope.
With MMC: the smaller pin gains 0.20 mm bonus and permits a Ø0.30 axis zone while preserving the Ø12.20 virtual condition.
Without MMC Fixed geometric tolerance
When the pin diameter is Ø11.90,the permitted axis zone remains Ø0.10.
Pin Ø11.90Permitted zone Ø0.10Envelope Ø12.00Diametrical clearance 0.20
With MMC Size-dependent allowance
When the pin diameter is Ø11.90,MMC permits a Ø0.30 axis zone.
Pin Ø11.90Permitted zone Ø0.30Envelope Ø12.20Diametrical clearance 0.00
Practical benefit: MMC lets manufacturing use the room released by a smaller pin for more geometric variation, while preserving the functional boundary. The size limits remain unchanged.
Inspection: passing the Ø12.20 bore alone does not prove the fixed Ø0.10 requirement without MMC; check perpendicularity separately. With MMC, a correctly designed functional gauge checks the combined boundary relative to A. Verify size limits in both cases.
03 / DRAWING
How to apply and read the annotation
Drawing callout
This example locates a clearance hole from two perpendicular datum faces using position at MMC.
Steps to add it to a drawing
Set the hole size limits and its basic location.
Use position with Ⓜ immediately after the diametrical tolerance.
Reference primary datum A, then secondary datum B.
Verify size, position and the resulting functional boundary.
How to read it
For a Ø10.1 ±0.1 hole, MMC is Ø10.0. Position Ø0.2 Ⓜ permits Ø0.2 at MMC. At Ø10.1, bonus is 0.1, so the total permitted position tolerance is Ø0.3.
For a hole or internal feature, MMC is the smallest permitted size.
For a pin or external feature, MMC is the largest permitted size.
Why A then B?
The two perpendicular datum faces orient the part and establish the hole’s basic height and lateral location. Translation along this through-hole axis does not affect its position, so a third datum is unnecessary here. A and B are planar faces, referenced without material-boundary modifiers.
APPLY THE EXAMPLE
MMC position tolerance calculator
For a cylindrical hole or shaft with position specified at MMC. All position tolerances are diametrical. Actual size must remain inside its size limits.
MMC diameter
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Bonus tolerance (diametrical)
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Total position tolerance (diametrical)
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Virtual-condition diameter
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Calculation steps
ASME Y14.5-2018 (R2024)
This page explains MMC using ASME Y14.5. Verify the edition specified on the engineering drawing and evaluate size, geometry and datum establishment together.
