GD&T (ASTM Y14.5)

Geometric Dimensioning and Tolerances: Symbols (ASTM Y14.5-2009)

Angularity – The condition of a surface, centerplane or axis being exactly at a specified angle
Circularity – A condition where all points of a surface of revolution, at any section perpendicular to a common axis, are equidistant from that axis.
Concentricity – The condition where the median points of all diametrically opposed elements of a cylinder (or a surface of revolution) are congruent with the axis of a datum feature.
Cylindricity – A condition of a surface of revolution in which all points of the surface are equidistant from a common axis.

Flatness – The condition of a surface having all of its elements in one plane.

Parallelism – The condition that results when a surface, axis or centerplane is exactly parallel to a datum.
Perpendicularity – The condition that results when a surface, axis, or centerplane is exactly 90° to a datum.
PositionThe zone within which the axis or center plane of a feature is permitted to vary from true (theoretically exact) position.
Profile of a Line Control – A geometric tolerance that limits the amount of error for line elements relative to their true profile.
Profile of a Surface Control – A geometric tolerance that limits the amount of error a surface can have relative to its true profile.
Circular RunoutA composite control that affects the form, orientation, and location of circular elements of a part feature relative to a datum axis.
Straightness (Axis or Centerplane) – The condition where an axis is a straight line (or, in the case of a centerplane, each line element is a straight line).
Symmetry – The condition where the median points of all opposed elements of two or more feature surfaces are congruent with the axis or centerplane of a datum feature.
Total Runout – A composite control affecting the form, orientation, and location of all surface elements of a diameter (or surface) relative to a datum axis.

Geometric Dimensionsing and Tolerances: Modifiers (ASTM Y14.5-2009)

All-Around Symbol – A circle placed on the bend of the leader line of a profile control.
Basic Dimension – A numerical value used to describe the theoretically exact size, true profile, orientation, or location of a feature or datum target.
Between Symbol – A double ended arrow that indicates the tolerance zone extends to include multiple surfaces.
Controlled Radius – A radius with no flats or reversals allowed. The symbol for a controlled radius is “CR.”
Datum Feature – A part feature that contacts a datum.
Datum Target – A symbol that describes the shape, size, and location of gage elements that are used to establish datum planes or axes.
Feature Control Frame – A rectangular box that is divided into compartments within which the geometric characteristic symbol, tolerance value, modifiers, and datum references are placed.
Least Material Condition – The condition in which a feature of size contains the least amount of material everywhere within the stated limits of size.
Maximum Material Condition – The condition in which a feature of size contains the maximum amount of material everywhere within the stated limits of size.
Projected Tolerance Zone – A tolerance zone that is projected above the part surface.
Radius – A straight line extending from the center of an arc or circle to its surface.

Reference Specification ASTM Y14.5-2009

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