The symbol Ⓜ is a standard modifier used in Geometric Dimensioning and Tolerancing (GD&T) as defined by the ASME Y14.5 standard. It represents Maximum Material Condition (MMC). MMC is the state of a feature of size where it contains the most material allowed by its tolerance limits. For an external feature like a shaft, this is its largest diameter. For an internal feature like a hole, it is its smallest diameter. Applying the MMC modifier to a geometric tolerance allows for an increase in the stated tolerance (a "bonus tolerance") as the feature's actual size departs from its MMC limit, which is critical for ensuring the assembly of mating parts.

A. The symbol for minimum material condition (LMC) is a circled L (Ⓛ), which represents the state of least material.

B. "Minimum measured condition" is not a standard, defined term or symbol within the ASME Y14.5 GD&T framework.

D. "Maximum measured condition" is not a standard, defined term or symbol within the ASME Y14.5 GD&T framework.

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1. ASME Y14.5-2018

Dimensioning and Tolerancing. The American Society of Mechanical Engineers.

Section 3.3.2

"Maximum Material Condition Symbol": "The symbol for maximum material condition is a capital letter M enclosed in a circle."

Section 2.8.1

"Maximum Material Condition (MMC)": "The condition in which a feature of size contains the maximum amount of material everywhere within the stated limits of size (e.g.

minimum hole diameter

maximum shaft diameter)."

2. ASQ Quality Press. (2017). The Certified Quality Engineer Handbook (4th ed.).

Chapter 21

Section V.B.3

"Material Condition Modifiers": This section explicitly defines the symbols for material condition. It states

"The symbol for maximum material condition (MMC) is Ⓜ."

3. Krulikowski

A. (1994). A comprehensive guide to geometric dimensioning and tolerancing. Purdue University Press.

Chapter 4

"Modifiers": "The symbol for maximum material condition is a capital M in a circle. Maximum material condition is the condition where a feature of size has the most material." (p. 29).