Maximum material condition (Ⓜ)
Ⓜ, a capital M in a circle, is the maximum material condition modifier. After a tolerance, it means the tolerance applies when the feature holds the most material, the smallest hole or the largest pin, and grows as the feature departs from that size.
Easily confused with
How to read it
Maximum material condition is the size at which a feature contains the most material allowed: the largest size of an external feature such as a pin, and the smallest size of an internal feature such as a hole (Illinois ME 170 notes; Berez, UNC Charlotte). Cogorno’s guide explains what the modifier adds: the stated tolerance applies at that size, and a bonus tolerance becomes available as the actual size departs from it toward the least material condition. The National Physical Laboratory’s guide says the principle exists for assembly, the smallest hole meeting the largest pin. The symbol can follow the tolerance or a datum letter in the frame (NPL).
Also searched as: Ⓜ, maximum material condition gd&t, maximum material condition symbol, mmc, mmc symbol.
This explains what a symbol specifies on a drawing. It isn't inspection or design guidance; the drawing and the edition of the standard it cites take precedence.
On a datum letter
After a datum letter, ASME Y14.5 calls the circled M a maximum material boundary (MMB); datum features of size can apply at regardless of material boundary, maximum material boundary or least material boundary (Cogorno). Keyence’s comparison lists the maximum material boundary as an ASME term with no ISO counterpart.
With no modifier
With no modifier in the frame, regardless of feature size (RFS) applies: the tolerance is the same at any size (Cogorno). The older circled S for RFS, from ANSI standards, was removed in ASME Y14.5-2009 (Keyence).
Differences by standard
ISO calls the same symbol the maximum material requirement (Keyence); NPL’s guide cites ISO 2692 on the maximum material principle.
Look-alikes
Least material condition Ⓛ is the circled L, the opposite end of the size range. Unicode encodes the circled letter as Ⓜ (U+24C2) CIRCLED LATIN CAPITAL LETTER M.
Read next
- Next in GD&T symbolsLeast material condition (Ⓛ)Ⓛ, a capital L in a circle, is the least material condition modifier: the tolerance applies when the feature holds the least material, the largest hole or the smallest pin, and grows as it departs from that size.
- The same shape in AI labels and iconsAI iconAI-generated or AI-changed content. A badge with the letters AI, often in a circle or beside a word such as generated or modified, labels an image, video, sound or text as made or altered with artificial intelligence. The European Union publishes an official set of these icons.
More GD&T symbols
The same shape elsewhere
Browse symbols drawn with circles or letters and numbers.
Sources
- Fundamentals of Geometric Dimensioning and Tolerancing (GD&T), Part I, Jaime Berez, seminar adapted from an undergraduate mechanical engineering course, version 2.1.0, 2023, Center for Precision Metrology, University of North Carolina at Charlotte (Zenodo), Slide 45
- Engineering Drawing Notes, Unit 8: Terms and Symbols (Part C, Geometric Dimensioning & Tolerancing), ME 170, fall 2019, Grainger College of Engineering, University of Illinois Urbana-Champaign, Unit 8, Supplementary symbols
- Geometric Dimensioning and Tolerancing for Mechanical Design: Instructors’ Guide, Gene R. Cogorno, guide to the McGraw-Hill textbook, rev. 10/12/2020, Technical Training Consultants, Chapters 3, 4 and 7, review answers
- Fundamental Good Practice in the Design and Interpretation of Engineering Drawings for Measurement Processes, Measurement Good Practice Guide No. 79, David Flack and Keith Bevan, 2005, National Physical Laboratory (UK), Chapter 4, Maximum material condition
- GD&T Symbols, GD&T Fundamentals, KEYENCE America, Associated Symbols
- Maximum Material Condition (MMC), GD&T Fundamentals, KEYENCE America, What Is M?
- Enclosed Alphanumerics: Range 2460–24FF (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, U+24C2
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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