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GD&T
Symbols, Terms and Definitions
ASME Y14.5M-1994
(Dimensioning and Tolerancing)
Common
Terms and Definitions
Profile Tolerances
Orientation
Tolerances
Locational Tolerances
Runout Tolerances
Form Tolerances
COMMON
TERMS AND DEFINITIONS
Basic
Dimension
A numerical value used to describe the theoretically exact size, profile,
orientation, or location of a feature or datum target. It is the basis
from which permissible variations are established by tolerances on other
dimensions, in notes, or in feature control frames.
Datum
A theoretically exact point, axis, or plane derived from the true
geometric counterpart of a specified datum feature. A datum is the origin
from which the location or geometric characteristics of features of a
part are established.
 
Datum Target
A specific line, or area on a part used to establish a datum.
Maximum
Material Condition (MMC)
The condition in which a feature of size contains the maximum amount
of material within the stated limits of size-for example, minimum hole
diameter, maximum shaft diameter.
Least
Material Condition (LMC)
The condition in which a feature of size contains the least amount
of material within the stated limits of size-for example, maximum hole
diameter, minimum shaft diameter.
Regardless
of Feature Size (RFS):
The term used to indicate that a geometric tolerance or datum reference
applies at any increment of size of the feature within its size tolerance.
Full Indicator
Movement
The total movement of an indicator when appropriately applied to a
surface to measure its variations (formerly called total indicator
reading-TIR).
Virtual Condition
The boundary generated by the collective effects of the specified
MMC limit of size of a feature and any applicable geometric tolerances.
Feature
Control Frame
The feature control frame consists of: A) type of control (geometric
characteristic), B) tolerance zone, C) tolerance zone modifiers (i.e.,
MMC or RFS), D) datum references if applicable and any datum reference
modifiers.
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PROFILE
TOLERANCES
Profile
of a Line
A uniform two dimensional zone limited by two parallel zone lines
extending along the length of a feature.
Profile
of a Surface
A uniform three dimensional zone contained between two envelope surfaces
separated by the tolerance zone across the entire length of a surface.
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ORIENTATION
TOLERANCES
Angularity
The distance between two parallel planes, inclined at a specified
basic angle in which the surface, axis, or center plane of the feature
must lie.
Perpendicularity (squareness)
The condition of a surface, axis, median plane, or line which is
exactly at 90 degrees with respect to a datum plane or axis.
Parallelism
The condition of a surface or axis which is equidistant at all points
from a datum of reference.
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LOCATIONAL
TOLERANCES
True
Position
A zone within which the center, axis, or center plane of a feature
of size is permitted to vary from its true (theoretically exact) position.
Concentricity
A cylindrical tolerance zone whose axis coincides with the datum
axis and within which all cross-sectional axes of the feature being controlled
must lie. (Note: Concentricity is very expensive and time-consuming
to measure. Recommended that you try position or runout as an alternative
tolerance.)
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RUNOUT
TOLERANCES
Runout
A composite tolerance used to control the relationship of one or
more features of a part to a datum axis during a full 360 degree rotation
about the datum axis.
Circular Runout
Each circular element of the feature/part must be within the runout
tolerance.
Total
Runout
All surface elements across the entire surface of the part must be
within the runout tolerance.
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FORM
TOLERANCES
Flatness
A two dimensional tolerance zone defined by two parallel planes within
which the entire surface must lie.
Straightness
A condition where an element of a surface or an axis is a straight
line.
Circularity
A condition on a surface of revolution (cylinder, cone, sphere) where
all points of the surface intersected by any plane perpendicular to a
common axis (cylinder, cone) or passing through a common center (sphere)
are equidistant from the axis of the center.
Cylindricity
A condition on a surface of revolution in which all points of the
surface are equidistant from a common axis.
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