Geometric Dimensioning and Tolerances: Symbols (ASTM Y14.52009)

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. 

Position – The 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 Runout – A 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 Y14.52009)

AllAround 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 Y14.52009