Geometric Dimensioning &
Tolerances
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Geometric Dimensioning & Tolerancing

uses standard symbols to indicate tolerances
that are based on the feature’s geometry.

sometimes called feature based dimensioning
& tolerancing or true position dimensioning &
tolerancing

uses feature control frames to indicate
tolerance
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G D & T Symbols
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Understanding Tolerance Zones

Traditional plus/minus type of tolerancing describes a
square zone for acceptable locations.
GD&T describes a zone around the theoretically exact
location for the feature.
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Basic Dimension

A theoretically exact
dimension used to
locate features in
GD&T
Basic dimensions
are untoleranced.
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Datums

Datums are features
on the object that are
used as reference
surfaces from which
other measurements
are made.
Not every GD&T
feature requires a
datum.
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Cylindrical Tolerance Zone
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Circular Runout
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Circular Runout
Controls single circular elements of a
surface
Controls circularity and coaxiality (two
or more features share a common axis)
Used to control wobbling motion
Measured by full indicator movement
(FIM) of a dial indicator

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Total Runout
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Total Runout

Provides combined control of a surface
element
Controls circularity, straightness, coaxiality,
angularity, taper, and profile or cylindrical
objects
May be used to control wobble and flatness
along with concavity or convexity of surfaces
perpendicular to a datum
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Maximum Material Condition

Maximum material condition for a hole feature
is the smallest sized hole.

Maximum material condition for a shaft
feature is the largest shaft.

The maximum material condition modifier in a
feature control frame means that the
tolerance applies at max. material condition.
If the actual hole is larger than the smallest
allowable hole, a bonus tolerance can be
added to the stated tolerance value.
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Maximum Material Condition
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Angular Tolerances
Traditional methods for tolerancing angles require that angled surfaces
be very accurate near the vertex of the angle, but can vary more
along the length of the angled feature.
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GD&T Angular Tolerance Zones
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Concentricity
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Summary

There are several methods you can use to
specify tolerances in a drawing.

Limit tolerances give the upper and lower
range for a dimension

Plus/minus tolerances give the nominal or
basic size and a plus and/or minus range for
the tolerance.

GD&T uses symbols to describe tolerance
zones based on geometric features.
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