Chapter 2 Dimensioning and Tolerancing Symbology 31
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symbol indicates that a dimension or tolerance
applies across interruptions in a feature of size so
that it acts as a single continuous feature. A con-
tinuous feature is sometimes referred to in indus-
try as an interrupted feature or a controlled feature.
Past practices sometimes used an extension line to
indicate a continuous feature, but that practice is
not supported by the current standard.
Other Symbols
Every geometric tolerance applied to a feature
of size is applicable regardless of that feature’s size
unless a modifi er is shown that requires the toler-
ance be applicable at a specifi c material condition.
In a similar way, every datum feature reference is
applicable regardless of material boundary unless
the datum feature reference is modifi ed to apply
at a specifi c material boundary. The applicable
material or boundary condition is specifi ed with
symbology shown in the tolerance specifi cation
(feature control frame), or it is implied on the basis
of rules that are defi ned in later chapters.
There are two material condition modifi er
symbols defi ned by the standard, and they are used
to indicate the material condition or the boundary
condition that is applicable. The same symbol (let-
ter M inside a circle) is used for both maximum
material condition (MMC) and maximum material
boundary (MMB). Similarly, one symbol (letter
L inside a circle) is used for least material condi-
tion (LMC) and least material boundary (LMB). If
neither of these modifi ers is shown in a tolerance
specifi cation, the tolerance is assumed to apply
regardless of feature size (RFS). There is no modi-
fi er symbol for RFS. If neither of the symbols is
applied in a datum feature reference, the datum
feature is assumed to apply regardless of material
boundary (RMB).
Material condition modifi er symbols are used
in tolerance specifi cations in CAD models and on
drawings. They are not typically used in drawing
notes or other written text because of font limita-
tions. Where it is necessary to reference a material
condition modifi er in written text, the term may be
spelled out or the appropriate abbreviation is used.
Some tolerance applications require the speci-
fi ed tolerance zone to project outside the object.
When this is necessary, a projected tolerance zone
symbol is used. See Figure 2-17. The projected tol-
erance zone symbol is the letter P within a circle.
Where tolerances applied on fl exible parts are
intended to apply in the free state, they are identi-
fi ed by the application of a free state symbol. The
free state symbol is the letter F inside a circle.
Tolerances that apply to a tangent plane instead
of to the surface are identifi ed by the tangent plane
symbol, a letter T inside a circle.
The letter U inside a circle is the unequally
disposed tolerance symbol. This symbol is shown
in a tolerance specifi cation to indicate that a profi le
tolerance is unequally disposed. The unequally
disposed zone may be a unilateral zone (entirely
to one side of the basic profi le) or a zone that is
Standards Advisory
MMB, LMB, RMB
The following was introduced in the ASME
Y14.5-2009 standard. When the MMC and
LMC symbols are used on datum feature ref-
erences, their meaning is expanded to include
maximum material boundary (MMB) and
least material boundary (LMB). MMB and
LMB may be applied to datum feature refer-
ences that are surfaces. Datum feature refer-
ences without a material boundary modifi er
symbol are assumed to apply regardless of
material boundary (RMB).
Translation
Independency
Maximum material condition
Maximum material boundary
Least material condition
Least material boundary
Projected tolerance zone
Free state
Tangent plane
Unequally disposed profile
All around
All over
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Figure 2-17. Modifi er symbols are primarily used
within feature control frames.