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 Y14.5-2009)

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

When it comes to machined parts, most people are typically concerned only with average roughness of a part, Ra; however, there are many more roughness parameters which can be specified.

Surface Finish usually takes on the lay of its manufacturing process.  For example, if a part is saw-cut, it will have a linear lay following

the travel of the saw teeth.  On the other hand, if a part is rotary-ground it’s finish will have a circular lay.

There are several specification guiding the detailing of surface finish.  The Europeans use BS EN ISO 1302:2002 Geometrical product specifications (GPS).  In the US, ASME Y14.36M is commonly used.  The symbols in each standard are quite similar:

The metric-to-inch conversion is:

Various machining operations have different typical surface finishes inherent to their respective manufacturing process, as indicated in the table below: