Glossary

A
ANSI Abbreviation for the American National Standards Institute. Previously known as the American Standards Association (ASA) and the United States of America Standards Institute (USASI). The organization is responsible for the standardization of the industrial standards in the United States of America.
Related pages
U.S. Standardization
ASA Abbreviation for the American Standards Association. Standardization organization for U.S. industries that dissolved in 1966. Currently renamed to ANSI.
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U.S. Standardization
ASME Abbreviation for the American Society of Mechanical Engineers. This global-scale organization for the engineering field holds academic conferences, publishes technical publications, and engages in technical standardization activities.
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U.S. Standardization
Autocollimator A non-contact optical measuring instrument that measures angles. The light from the light source is converted into parallel light and emitted out of the objective lens to the mirror on the upper side of the measurement target. The difference between the reflected light and emitted light is measured in arcseconds. An autocollimator can measure straightness, perpendicularity, flatness, and other characteristics.
B
Best fit capability A function that compares a product’s measurement data and 3D CAD data, and verifies the difference. The superimposed results are displayed as 3D images, on which you can see the deviation between the measurement data and CAD data.
Bonus tolerance A modification of a GD&T tolerance using maximum/least material conditions. This can reduce non-conformities products resulting from unnecessarily strict tolerance settings, as well as simplify inspections.
C
Composite positional tolerancing A method for specifying a different tolerance for the positions of the features relative to one another and the positions from a datum system. Even when there are multiple rows of feature control frames, a single geometric tolerance symbol is indicated in a linked frame. This enables a simultaneous specification of location, orientation, and form for the same feature.
Composite profile tolerancing A method for specifying a different tolerance for the profile tolerance from a datum system. Even when there are multiple rows of feature control frames, two geometric tolerance symbols are indicated in a linked frame. This enables a simultaneous specification of location, orientation, and form for the same feature.
D
Datum floating To not restrain the datum when the datum is a size feature and maximum material condition is applied to the datum.
Derived feature Center line, center plane, or center point derived from the integral feature.
E
External feature A feature that makes up the outer side of a machine part (e.g., the outer side of a cylinder shaft or cuboid).
Extracted feature A feature obtained through measurement.
G
General geometric tolerance Geometric tolerances collectively indicated instead of being individually indicated on a drawing, for geometric tolerances with no special functional requirement. Tolerance class (basic size tolerance class) symbols are defined based on accuracy.
General tolerance Tolerances collectively indicated instead of being individually indicated on a drawing, for dimensions (length, angle, chamfering dimensions) with no special functional requirement. Tolerance class (basic size tolerance class) symbols are defined based on accuracy.
GPS Abbreviation for Geometrical Product Specification. For the purpose of eliminating unclear drawings, systematically organizing measurement uncertainties, and applying a global certification system, TC213 of the ISO is working on standardization by adding to and amending existing international standards.
I
Integral feature A surface, or a line on a surface. A feature with actual form.
Internal feature A feature that makes up the inner side of a machine part (e.g. bores and grooves).
ISO Abbreviated name for the International Organization for Standardization. This non-governmental organization establishes internationally recognized standards, which are called ISO Standards.
J
JIS Abbreviation for Japanese Industrial Standards. JIS sets forth the standards and measurement methods for Japanese industrial products. JIS is established by the Japanese Industrial Standards Committee (JISC), which is part of the Ministry of Economy, Trade and Industry based on the Industrial Standardization Act.
L
Least Material Virtual Condition (LMVC) A state where the volume made by size tolerance and geometric tolerance becomes the smallest.
M
Mandrel A cylindrical bar with high precision in terms of size and geometrical characteristics.
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Types of Datums
Material condition A method of specifying a special relationship between dimensional tolerance (size tolerance) and geometric tolerance. This is indicated on drawings using the symbol or . Maximum material condition and least material condition are used to increase indicated geometric tolerances when there is a difference between the material condition and actual size.
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Feature Control Frame
Maximum Material Virtual Condition (MMVC) A state where the volume made by size tolerance and geometric tolerance becomes the greatest.
Mean diameter An indication that the average of measured values at two points on a circular or cylindrical form must be between the maximum allowable limit size value and minimum allowable limit size value. “AVG” is used for annotation.
N
Nominal value Mean value of actual measurement data obtained from measuring machines.
P
Perfect form A form with absolutely no geometrical deviation.
S
Spot facing Cutting the entry point of a bore by a larger diameter for the purpose of making the surface smooth in order to prevent the heads of bolts and screws from protruding or to reinforce tightening.
Related pages
U.S. Standardization
T
T.I.R An abbreviation for “Total Indicator Reading.” The difference between the maximum and minimum values in run-out measurement.
Taylor Principle The maximum material size of a workpiece must be inspected using a GO gauge accurately made to the workpiece’s maximum material size. The least material size of a workpiece must be inspected using a NO-GO gauge made to the same least material size of that workpiece and designed to individually inspect each element of the workpiece.
Related pages
U.S. Standardization
Tolerance class Tolerance values in the 0.01 mm to 0.09 mm or 0.001 mm to 0.009 mm ranges make it difficult to read indications. This standard is used to avoid this and write tolerance indications concisely. Tolerances are divided into classes by deviation from the reference dimension (specified size), and each class is given an upper-case or lower-case letter as a symbol.
V
Virtual size The dimension that defines the virtual condition of a feature. For external features:
Maximum allowable size + Orientation tolerance or Location tolerance
For internal features:
Minimum allowable size - Orientation tolerance or Location tolerance
Z
Zero geometric tolerance A method of presuming no geometrical deviation (zero geometrical deviation) under maximum virtual condition and adding the difference to geometric tolerance as a feature gets closer to the least virtual condition.

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