Glossary  

A

  
Associated Derived Feature Center point, axis or median plane derived from one or more associated integral features (ISO 14660).
Associated Integral Feature Feature of perfect form associated to the extracted integral feature in accordance with specified conventions (ISO 14660).
 

C

  
Common Datum Datum based on two or more surfaces considered simultaneously (ISO/CD 5459-1:1998).
 

D

  

Datum

 

 A theoretically exact point, axis, or plane derived from the true geometric counterpart of a specified datum feature. A datum is the origin from which the location or geometric characteristics of features of a part are established, (ASME Y14.5M-1994).

Situation feature used to define the position and/or orientation of a tolerance zone or to define the position and/or the orientation of the virtual conditions (in the case of the complementary requirements, e.g maximum material requirement), (ISO/CD 5459-1:1998(E)).
Datum System Ordered list of at least two datums and at most three datums, which may be single or common datums, (ISO/CD 5459-1:1998(E)).

Note: A datum-system is used to define the position and/or orientation of a tolerance zone or to define the position and/or the orientation of the virtual condition (in the case of complementary requirements, e.g maximum material requirement).
(Datum) Target A specified point, line, or area on a part used to establish a datum, (ASME Y14.5M-1994).

Portion of an integral feature (surface) which can be a point, a line or an area and which is used for establishing a datum, (ISO/CD 5459-1:1998(E)).
Datum Feature An actual feature of a part that is used to establish a datum, (ASME Y14.5M-1994).
Derived Feature Center point, median line or median surface from one or more integral features (ISO 14660)

Examples:

1- The center of a sphere is derived feature obtained from the sphere, which is an integral feature.

2 -The median line of a cylinder is a derived feature obtained from the cylindrical surface, which is an integral feature.
 

E

  
Extracted Derived Feature Center point, median line or median surface derived from one or more extracted integral features (ISO 14660).

Note: For convenience:

- the derived median line of an extracted cylindrical surface is called an extracted median line (see ISO 14660-2).

- the derived median surface of 2 opposite extracted planar surfaces is called an extracted median surface (see ISO 14660-2).
Extracted Integral Feature Approximated representation of the real (integral) feature, obtained by extracting a finite number of points from the real (integral) feature performed in accordance with specified conventions. (ISO 14660)

Note: This representation is defined according to the required function of the feature. Several such representations may exist for each real (integral) feature.
 

F

  
Feature The general term applied to a physical portion of a part, such as a surface, pin, tab, hole or slot, (ASME Y14.5M-1994).

Geometric feature, point, line or surface, (ISO 14660-1).
Feature of Size Geometric shape defined by a linear or angular dimension which is a size(ISO 14660)

Notes

1- The features of size can be a cylinder, a sphere, two parallel opposite surfaces, a cone or a wedge.

2-  In standards such as ISO 286-1 and ISO/R 1938 the terms plain workpiece and single features are used with a meaning close to "feature size".
 

G

  
Geometric Feature Point, line or surface (ISO 14660).
 

I

  
Integral Feature Surface or line on a surface (ISO 14660)

Note: An integral feature is intrinsically defined.
 

N

  
Nominal integral feature Theoretically exact integral feature as defined by a technical drawing or by other means (ISO 14660).
Nominal Derived Feature Center point, axis or median plane derived from one or more nominal integral features (ISO 14660)

Note: On the technical drawing nominal derived features are mostly represented by chain lines (dash-dotted lines).
 

R

  
Real (integral) Feature Integral feature part of a real surface of a workpiece limited by the adjacent real (integral) features (ISO 14660).

Note: No real derived feature exist.
Real Surface of a Workpiece Set of features which physically exist and separate the entire workpiece from the surrounding medium (ISO 14660).
Restricted Surface Portion of an integral feature (surface) which is an area and which is used for establishing a datum (ISO/CD 5459-1:1998)

Note: the area of a restricted surface is relatively large compared with the complete surface.
 

S

  
Single Datum Datum based on one surface considered alone (ISO/CD 5459-1:1998).
Situation Feature Ideal feature which is a point, a straight line, a plane or a helix, from which the position and/or the orientation of a feature can be defined (ISO/CD 5459-1:1998)

Note: Situation features are defined by and are characteristics of the class of surface involved.
Surface class Group of surfaces having the same degree of freedom for which the surfaces are unvarying, (ISO/CDIS 5459-1:1998(E)).
 

T

  
Tolerance zone Space limited by one or several geometrically perfect lines or surfaces, and characterized by a linear dimension, called a tolerance (ISO/FDIS 1101:2000(E))