GD&T terms and definitions

ASMEY 14.5-2009 Terminology

The following GD&T terms are defined in ASMEY 14.5-2009 Standard.

1.3.1 Angularity
Angularity is the condition of a surface, feature’s center plane, or feature’s axis at any specified angle from a datum plane or datum axis. See section 6.3.1.
1.3.2 Boundary, Inner
Boundary, Inner: a worst-case boundary generated by the smallest feature (MMC for an internal feature and LMC for an external feature) minus the stated geometric tolerance and any additional geometric tolerance (if applicable) resulting from the feature’s departure from its specified material condition. See Figs. 2-12 through 2-17.
1.3.3 Boundary, Least Material (LMB)
The limit defined by a tolerance or combination of tolerances that exists on or inside the material of a feature(s).
1.3.4 Boundary, Maximum Material (MMB)
The limit defined by a tolerance or combination of tolerances that exists on or outside the material of a feature(s).
1.3.5 Boundary, Outer
A worst-case boundary generated by the largest feature (LMC for an internal feature and MMC for an external feature) plus the stated geometric tolerance and any additional geometric tolerance (if applicable) resulting from the feature’s departure from its specified material condition. See Figs. 2-12 through 2-17.
1.3.6 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 or spine (curved line) are equidistant from that axis or spine.
(b) for a sphere, all points of the surface intersected by any plane passing through a common center are equidistant from that center.
1.3.7 Coaxiality
Coaxiality is that condition where the axes of the unrelated actual mating envelope, axis of the unrelated minimum material envelope, or median points, as applicable of one or more surfaces of revolution, are coincident with a datum axis or another feature axis. The amount of permissible variation from coaxiality may be expressed by a variety of means, including a positional tolerance, a runout tolerance, a concentricity tolerance, or a profile of a surface tolerance.
1.3.8 Complex Feature
A single surface of compound curvature or a collection of other features that constrains up to six degrees of freedom.
1.3.9 Concentricity
Concentricity is that condition where the median points of all diametrically opposed elements of a surface of revolution (or the median points of correspondingly located elements of two or more radially disposed features) are congruent with a datum axis (or center point).
1.3.10 Coplanarity
Coplanarity is the condition of two or more surfaces having all elements in one plane.
1.3.11 Constraint
A limit to one or more degrees of freedom.
1.3.12 Cylindricity
Cylindricity is a condition of a surface of revolution in which all points of the surface are equidistant from a common axis.
1.3.13 Datum
A theoretically exact point, axis, line, plane, or combination thereof derived from the theoretical datum feature simulator.
1.3.14 Datum Axis
The axis of a datum feature simulator established from the datum feature.
1.3.15 Datum Center Plane
The center plane of a datum feature simulator established from the datum feature.
1.3.16 Datum Feature
A feature that is identified with either a datum feature symbol or a datum target symbol.
1.3.17 Datum Feature Simulator
Encompasses two types: theoretical and physical.
1.3.17.1 Datum Feature Simulator (Theoretical)
The theoretically perfect boundary used to establish a datum from a specified datum feature.
NOTE: Whenever the term “datum feature simulator” is used in this Standard, it refers to the theoretical, unless specifically otherwise indicated.
1.3.17.2 Datum Feature Simulator (Physical)
The physical boundary used to establish a simulated datum from a specified datum feature.
NOTE: For example, a gage, fixture element, or digital data (such as machine tables, surface plates, a mandrel, or mathematical simulation) -although not true planes- are of sufficient quality that the planes derived from them are used to establish simulated datums. Physical datum feature simulators are used as the physical embodiment of the theoretical datum feature simulators during manufacturing and inspection. See ASME Y14.43.
1.3.18 Datum Reference Frame
A datum reference frame is three mutually perpendicular intersecting datum planes.
1.3.19 Datum, Simulated
A point, axis, line, or plane (or combination thereof) coincident with or derived from processing or inspection equipment, such as the following simulators: a surface plate, a gage surface, a mandrel, or mathematical simulation.
1.3.20 Datum Target
Datum targets are the designated points, lines, or areas that are used in establishing a datum. Datum targets are used in establishing a datum reference frame.
1.3.21 Diameter, Average
An average diameter is the average of several diametric measurements across a circular or cylindrical feature.
1.3.22 Dimension
A numerical value(s) or mathematical expression in appropriate units of measure used to define the form, size, orientation or location, of a part or feature.
1.3.23 Dimension, Basic
A theoretically exact dimension. NOTE: A basic dimension is indicated by one of the methods shown in Figs. 3-10 and 7-1.
1.3.24 Dimension, Reference
A dimension, usually without a tolerance, that is used for informational purposes only.
NOTE: A reference dimension is a repeat of a dimension or is derived from other values shown on the drawing or on related drawings.
1.3.25 Envelope, Actual Mating
this envelope is outside the material. A similar perfect feature(s) counterpart of smallest size that can be contracted about an external feature(s) or largest size that can be expanded within an internal feature(s) so that it coincides with the surface(s) at the highest points. Two types of actual mating envelopes - unrelated and related - are described in paras. 1.3.25.1 and 1.3.25.2.
1.3.25.1 Unrelated Actual Mating Envelope
A similar perfect feature(s) counterpart expanded within an internal feature(s) or contracted about an external feature(s), and not constrained to any datum(s). See Fig. 1-1.
1.3.25.2 Related Actual Mating Envelope
a similar perfect feature counterpart expanded within an internal feature(s) or contracted about an external feature(s) while constrained either in orientation or location or both to the applicable datum(s). See Fig. 1-1.
1.3.26 Envelope, Actual Minimum Material
This envelope is within the material. A similar perfect feature(s) counterpart of largest size that can be expanded within an external feature(s) or smallest size that can be contracted about an internal feature(s) so that it coincides with the surface(s) at the lowest points. Two types of actual minimum material envelopes - unrelated and related - are described in paras. 1.3.26.1 and 1.3.26.2.
1.3.26.1 Unrelated Actual Minimum Material Envelope
a similar perfect feature(s) counterpart contracted about an internal feature(s) or expanded within an external feature(s), and not constrained to any datum reference frame. See Fig. 1-2.
1.3.26.2 Related Actual Minimum Material Envelope
a similar perfect feature(s) counterpart contracted about an internal feature(s) or expanded within an external feature(s) while constrained in either orientation or location or both to the applicable datum(s). See Fig. 1-2.
1.3.27 Feature
A physical portion of a part such as a surface, pin, hole, or slot or its representation on drawings, models, or digital data files.
1.3.28 Feature Axis
the axis of the unrelated actual mating envelope of a feature.
NOTE: In this Standard, when the term “feature axis” is used, it refers to the axis of the unrelated actual mating envelope unless specified otherwise.
1.3.29 Feature, Center Plane of
The center plane of the unrelated actual mating envelope of a feature.
NOTE: In this Standard, when the term “feature center plane” is used, it refers to the center plane of the unrelated actual mating envelope unless specified otherwise.
1.3.30 Derived Median Plane
an imperfect (abstract) plane formed by the center points of all line segments bounded by the feature. These line segments are normal (perpendicular) to the center plane of the unrelated actual mating envelope.
1.3.31 Derived Median Line
An imperfect (abstract) line formed by the center points of all cross sections of the feature. These cross sections are normal (perpendicular) to the axis of the unrelated actual mating envelope.
1.3.32 Feature of Size
Encompasses two types: regular and irregular. See sections 1.3.32.1 and 1.3.32.2.
1.3.32.1 Regular Feature of Size
one cylindrical or spherical surface, a circular element, and a set of two opposed parallel elements or opposed parallel surfaces, each of which is associated with a directly toleranced dimension. See section 2.2.
1.3.32.2 Irregular Feature of Size.
the two types of irregular features of size are as follows:
(a) a directly toleranced feature or collection of features that may contain or be contained by an actual mating envelope that is a sphere, cylinder, or pair of parallel planes.
(b) a directly toleranced feature or collection of features that may contain or be contained by an actual mating envelope other than a sphere, cylinder, or pair of parallel planes.
1.3.33 Feature Control Frame
A feature control frame is a rectangle divided into compartments containing the geometric characteristic symbol followed by the tolerance value or description, modifiers, and any applicable datum feature references. See Figs. 3-23, 4-2, and 7-4. Where applicable, the tolerance is preceded by the diameter or spherical diameter symbol and followed by a material condition modifier.
1.3.34 Feature-Relating Tolerance Zone Framework (FRTZF)
The tolerance zone framework(s) that controls the basic relationship between the features in a pattern with that framework constrained in rotational degrees of freedom relative to any referenced datum features.
1.3.35 Free State
The condition of a part free of applied forces.
1.3.36 Free-State Variation
Free-state variation is the distortion of a part after removal of forces applied during manufacture. This distortion is principally due to weight and flexibility of the part and the release of internal stresses resulting from fabrication.
1.3.36 Free-State Variation
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1.3.37 Flatness
Flatness is the condition of a surface or derived median plane having all elements in one plane.
1.3.38 Least Material Condition (LMC)
The condition in which a feature of size contains the least amount of material within the stated limits of size (e.g., maximum hole diameter, minimum shaft diameter).
1.3.39 Maximum Material Condition (MMC)
The condition in which a feature of size contains the maximum amount of material within the stated limits of size (e.g., minimum hole diameter, maximum shaft diameter).
1.3.40 Non-Uniform Tolerance Zone
A non-uniform tolerance zone is a maximum material boundary and a least material boundary, of unique shape, that encompasses the true profile. These boundaries are defined in a CAD file or by basic dimensions on a drawing with phantom lines to indicate the tolerance zone.
1.3.41 Parallelism
Parallelism is the condition of a surface or feature’s center plane, equidistant at all points from a datum plane; or a feature’s axis, equidistant along its length from one or more datum planes or datum axis. See Fig. 3-1.
1.3.42 Pattern
two or more features or features of size to which a locational geometric tolerance is applied and are grouped by one of the following methods: nX, n COAXIAL HOLES, ALL OVER, ----- B, n SURFACES, simultaneous requirements, or INDICATED.
1.3.43 Pattern-Locating Tolerance Zone Framework (PLTZF)
The tolerance zone framework that controls the basic relationship between the features in a pattern with that framework constrained in translational and rotational degrees of freedom relative to the referenced datum features.
1.3.44 Perpendicularity
Perpendicularity is the condition of a surface, feature’s center plane, or feature’s axis at a right angle to a datum plane or datum axis. See Fig. 3-1.
1.3.45 Plane, Tangent
A plane that contacts the high points of the specified feature surface.
1.3.46 Position
Position is the location of one or more features of size relative to one another or to one or more datums.
1.3.47 Profile
A profile is an outline of a surface, a shape made up of one or more features, or a two-dimensional element of one or more features.
1.3.48 Regardless of Feature Size (RFS)
Indicates a geometric tolerance applies at any increment of size of the actual mating envelope of the feature of size.
1.3.49 Regardless of Material Boundary (RMB)
Indicates that a datum feature simulator progresses from MMB toward LMB until it makes maximum contact with the extremities of a feature(s).
1.3.50 Restraint
the application of force(s) to a part to simulate its assembly or functional condition resulting in possible distortion of a part from its free-state condition. See section 4.20.
1.3.51 Resultant Condition
The single worst-case boundary generated by the collective effects of a feature of the size’s specified MMC or LMC, the geometric tolerance for that material condition, the size tolerance, and the additional geometric tolerance derived from the feature’s departure from its specified material condition. See Figs. 2-12, 2-13, 2-15, and 2-16.
1.3.52 Runout
Runout is a tolerance used to control the functional relationship of one or more features to a datum axis established from a datum feature specified at RMB.
1.3.53 Simultaneous Requirement
A simultaneous requirement is where two or more geometric tolerances apply as a single pattern or part requirement. A simultaneous requirement applies to position and profile tolerances that are located by basic dimensions, related to common datum features referenced in the same order of precedence at the same boundary conditions.
1.3.54 Size, Actual Local
The measured value of any individual distance at any cross section of a feature of size. See Fig. 1-1.
1.3.55 Size, Limits of
The specified maximum and minimum sizes. See para. 2.7.
1.3.56 Size, Nominal
The designation used for purposes of general identification.
1.3.57 Straightness
Straightness is a condition where an element of a surface, or derived median line, is a straight line.
1.3.58 Statistical Tolerancing
Statistical tolerancing is the assigning of tolerances to related components of an assembly on the basis of sound statistics (such as the assembly tolerance is equal to the square root of the sum of the squares of the individual tolerances).
1.3.59 Symmetry
Symmetry is that condition where the median points of all opposed or correspondingly located elements of two or more feature surfaces are congruent with a datum axis or center plane.
1.3.60 Tolerance
The total amount a specific dimension is permitted to vary. The tolerance is the difference between the maximum and minimum limits.
1.3.61 Tolerance, Bilateral
A tolerance in which variation is permitted in both directions from the specified dimension.
1.3.62 Tolerance, Geometric
The general term applied to the category of tolerances used to control size, form, profile, orientation, location, and runout.
1.3.63 Tolerance, Unilateral
A tolerance in which variation is permitted in one direction from the specified dimension.
1.3.64 True Position
The theoretically exact location of a feature of size, as established by basic dimensions.
1.3.65 True Profile
A true profile is a profile defined by basic radii, basic angular dimensions, basic coordinate dimensions, basic size dimensions, undimensioned drawings, formulas, or mathematical data, including design models.
1.3.66 Uniform Tolerance Zone
A uniform tolerance zone is the distance between two boundaries equally or unequally disposed about the true profile or entirely disposed on one side of the true profile.
1.3.67 Virtual Condition
a constant boundary generated by the collective effects of a considered feature of the size’s specified MMC or LMC and the geometric tolerance for that material condition. See Figs. 2-12, 2-13, 2-15, and 2-16.

ISO Geometrical Tolerancing Glossary

The following terms are related to ISO geometrical tolerancing. The definitions are from ISO 1101:2004 and its companion published standards.

Actual Size
The size of a feature, obtained by measurement (ISO 286-1:1998)
Actual Local Size
Any individual distance at any cross section of a feature, i.e. any size measured between any opposed points (ISO 2692:2006)
Angular Dimension
The angle between two features or the angle of an angular feature of size (ISO 129-1:2004)
Angularity Tolerance
A geometrical tolerance that defines the allowable deviation from the exact (TED) angle
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