Glossary

Actual Size: The general term of a produced feature. This term includes the actual mating size and the actual local sizes.

Actual Local Size: The value of any individual distance at any cross section of a feature.

Actual Mating Size: The dimensional value of the actual mating envelope.

Attitude Tolerance: See Orientation Tolerance. Actual Mating Envelope: The term is defined according to the type of features, as follows,
a) For an external feature. A similar perfect feature counterpart of smallest size which can be circumscribed about the feature so that it just contacts the surface at the highest points. For example, a smallest cylinder of perfect from to two parallel planes of perfect form at minimum separation which just contact (s) the highest points of the surfaces (s). For features controlled by orientation or positional tolerances, the actual mating envelope is oriented relative to the appropriate datum (s); e.g., perpendicular to a primary datum plane.
b) For an internal feature, a similar perfect feature counterpart of largest size which can be inscribed within the feature so that if just contact the surface at the highest points. For example, a largest cylinder of perfect from or two parallel planers of perfect from at maximum separation which just contact (s) the highest points of the surface (s). For features controlled by orientation or positional tolerances, the actual mating envelope is oriented relative to the appropriate datum (s): e.g., perpendicular to a primary datum plane.
Basic Dimension: A dimension specified on a drawing as BASIC (or abbreviated BSC) is 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. A basic dimension is symbolized by boxing it.

Circular Run out: Circular run out is the composite control of circular elements of a surface independently at any circular measuring position as the pair is rotated through 360°.

Circularity (Roundness) – Circularity is a condition of a surface where:
a) For a feature other than a sphere, All points of the surface intersected by any plane perpendicular to an axis are equidistant form that axis.
b) For a sphere, All points of the surface intersected by any plane passing through a common center are equidistant from that center.

Coaxiality: Coaxiality of features exists when two or more features have coincident axes, i.e., a feature axis and a datum feature axis.

Concentricity: Concentricity is that condition where the median points diametrically opposed elements of a figure of revolution (or correspondingly located elements of two or more radially – disposed features) are congruent with the axis (or center points) of a datum feature.

Cylindricity: Cylindricity is a condition of a surface of revolution in which all points of the surface are equidistant from a common axis.

Datum Feature: A datum feature is an actual (physical) feature of a part used to establish a datum.

Datum Feature Simulator: A Surface of adequately precise (such as a surface plate, a gage surface, or a mandrel) contacting the datum feature (s) and used to establish the simulated datums during manufacture and inspection.

Datum, Simulated: A points axis, or plane established by processing or inspection equipment such as the following simulators: a surface plate, a gage surface, or a mandrel.

Datum Feature Symbol: The datum feature symbol consists of a capital letter enclosed in a square frame, a leader line extending from the frame to the concerned feature and terminating with a triangle,

Datum Line: A datum line is that which has length but no breadth or depth such as the intersection line of two planes, center line or axis of hole or cylinders, reference line for tooling, gaging, or datum target