Maximum material condition

Meaning and applicability

Maximum material condition (MMC) is the smallest permitted hole or largest permitted shaft. A feature modifier links the geometric allowance to size. KEYENCE MMC tutorial

In the ideal hole example, size limits are 10.00–10.20 mm and position tolerance is 0.20 mm in diameter at MMC. At 10.12 mm, the 0.12 mm departure from MMC gives 0.32 mm zone diameter and 0.16 mm radial displacement. A fixed ideal datum frame and parallel ideal axis are assumed.

Specify the governing standard and edition. For ISO GPS, ISO 2692:2021, edition 4, June 2021, defines maximum material requirement (MMR), least material requirement and reciprocity requirement. Its public scope limits those requirements to linear features of size of cylindrical type or two parallel opposite planes type. ISO reports confirmation on October 5, 2026; that confirmation does not create a new technical edition. Assembly is a stated MMR application, not its only possible function. ISO 2692 record and scope

ASME lists Y14.5-2018 (R2024) for dimensioning and tolerancing. Use the drawing's governing framework, including its size and datum rules. A tutorial's MMC shorthand and ISO's MMR terminology do not establish that all defaults or evaluation methods are interchangeable. ASME Y14.5 record

Read the whole indication

A circled M following the geometric tolerance value applies a material requirement to the controlled feature. A circled M following a datum reference has a different role. KEYENCE shows these as separate placements. Preserve the symbol's attachment when transferring requirements into a model, inspection program or supplier instruction. KEYENCE modifier placement

Before calculating, identify the feature and its size limits, tolerance characteristic, zone shape, datum sequence and every modifier. “Position 0.20 at MMC” remains incomplete if the required diametrical zone or datum references are missing. Do not treat a diametrical position allowance as the same numerical radial displacement.

MMC is not a blanket modifier for any surface or geometric characteristic. Confirm that the selected feature and control allow it under the governing standard. A software menu containing additional feature types does not expand ISO 2692's stated scope.

Bonus tolerance and the required size

PC-DMIS 2023.1 documents additional position tolerance as departure of the unrelated mating envelope size from MMC. It also separates the mathematics deriving the controlled feature from those establishing the datums. This is a named implementation, not a claim that every diameter reported by every instrument supplies the required size. Hexagon position, allowed modifiers and options

Hexagon's associated size documentation distinguishes envelope-based and least-squares calculations. For its DEFAULT feature mathematics, the measured bonus uses an appropriate inscribed or circumscribed fit; its LSQ option uses a least-squares global size. These choices can matter when a real feature has form error. Record the selected method and its suitability for the measurement task. PC-DMIS 2023.1 size evaluation

A convenient caliper reading or average circle diameter must not silently replace the required envelope characteristic. Conversely, a software result should not be described as an exact physical envelope without considering its fitting method, sampled data and measurement uncertainty.

Original ideal-hole example

Assume a perfectly cylindrical hole with limits 10.00–10.20 mm, controlled by a diametrical position tolerance of 0.20 mm at MMC. Assume a fixed ideal datum frame, no datum mobility and no axis tilt. The hole's MMC is 10.00 mm.

For an actual ideal diameter of 10.12 mm:

bonus = 10.12 − 10.00 = 0.12 mm

total position-zone diameter = 0.20 + 0.12 = 0.32 mm

The permitted radial axis displacement is half that diameter: 0.16 mm. At MMC, it is 0.10 mm. These values are original explanatory choices, not recommended production tolerances.

For this simple internal-feature case, the virtual-condition diameter is:

internal virtual condition = MMC diameter − geometric tolerance at MMC

10.00 − 0.20 = 9.80 mm.

KEYENCE's glossary gives the corresponding internal virtual-size relationship and, for external features, the opposite sign: maximum allowable size plus the applicable orientation or location tolerance. These are simple boundary relationships, not a complete functional-gauge design specification. KEYENCE virtual-size definitions

The example reconciles geometrically:

An ideal 9.80 mm cylindrical boundary centered on the nominal axis is therefore preserved in both cases. This demonstrates the size–position tradeoff. It does not alone prove assembly of a complete mechanism: the mating part's geometry, other features, datum relationships and applicable simultaneous requirements also matter. Real form error and tilt are excluded here and require the full specified evaluation.

Feature allowance versus datum boundary

In the ASME-oriented datum controls documented by PC-DMIS 2023.1, an unmodified datum reference is RMB, regardless of material boundary; a maximum-material datum reference uses MMB, maximum material boundary. The documentation cautions that a specified material boundary size is not simply the datum feature's nominal or MMC size. PC-DMIS datum modifiers

Do not add a guessed “datum bonus” to the 0.32 mm result above. Any permitted datum-related mobility must respect the applicable boundary and remaining constraints. A controlled-feature allowance and datum-frame establishment are separate parts of the evaluation. If a drawing uses both modifiers, retain both in the inspection definition rather than collapsing them into one unexplained number.

Handoff and acceptance

Preserve the drawing revision and governing standard; feature identity and limits; complete tolerance indication; datum references and modifiers; required size characteristic; and measurement/evaluation method. A useful report distinguishes the specified tolerance, measured size, calculated allowance and geometric result.

Size acceptance remains necessary even when position is within the calculated allowance. A functional gauge that demonstrates one boundary relationship does not automatically verify every size limit or unrelated characteristic. When supplier and customer results differ, compare feature construction, surface sampling, size mathematics and datum establishment before concluding that their numerical position results represent the same evaluation.

Source versions

Sources checked include ISO 2692:2021, ASME Y14.5-2018 (R2024), and release-specific PC-DMIS 2023.1 documentation. Hexagon's Position page prints March 8, 2023. No technical revision date is inferred for KEYENCE's live tutorials from their copyright footer. The worked calculation and proposed handoff guidance are original explanations.

Least material condition · Datum reference frames · Dimensions, tolerances and specifications