Geometric dimensioning and tolerancing
(GD&T) is used to define the nominal
(theoretically perfect) geometry of parts
and assemblies, to define the allowable
variation in form and possible size of
individual features, and to define the
allowable variation between features.

Angularity
 the condition of a surface or axis at a
specified angle (other than 90 degrees) from
a datum plane or axis. The angle must be
basic.
Circularity
 a condition of a surface of revolution
where (a) for a cylinder of cone, all points
of the surface intersected by any plane
perpendicular to common axis are equidistant
from the axis; (b) for a sphere, all points
of the service intersected by any plane
passing through a common center are
equidistant from the center.
Concentricity
 a condition where the axes of all
crosssectional elements of a surface of
revolution are common to the axis of a datum
feature.
Cylindricity
 a condition of the surface of revolution
in which all points of the surface are
equidistant from a common axis.
Flatness
 t he condition of a surface having all
elements in one place.
Parallelism
 a condition of a surface equidistant at
all points from a datum plane. Or an axis
equidistant along its length to datum axis.
Perpendicularity  the
condition of a surface, median plane, or
axis at a right angle to a datum plane or
axis.
Position
 defines a zone within which the center
axis, or center plane, of a feature of size
is permitted to vary from true
(theoretically exact) position.
Profile of Line
 the tolerance zone established by the
profile of a line tolerance extending along
the length of the considered feature on
single elements.
Profile of
Surface  the tolerance zone
established by the profile of a surface
tolerance is three dimensional, extending
along the length and width (or
circumference) of the considered feature or
features.
Runout,
Circular  controls singular
line elements on the surface of a feature
related to a datum(s).
Runout, Total
 controls full surface (FIM) variations on
the full surface of a feature related to
datum(s).
Straightness
 a condition where an element of a
surface of an axis is a straight line.
