Angularity

That condition of a surface, feature's

center plane, or feature's axis at any specified angle from

a datum plane or datum axis.

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.

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).

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).

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.

Circularity (Roundness)

(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.

Coaxiality

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.

Complex Feature

A single surface of compound curvature or a collection of other features that constrains up to six degrees of freedom.

Concentricity

 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).

Coplanarity

That condition of two or more surfaces having all elements in one plane. 

Constraint

A limit to one or more degrees of freedom.

Cylindricity

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

Datum

A theoretically exact point, axis, line, plane or combination thereof derived from the theoretical datum feature simulator.

Datum Axis

The axis of a datum feature simulator established from the datum feature.

Datum Center Plane

The center plane of a datum feature simulator established from the datum feature.

Datum Feature

A feature that is identified with either a datum feature symbol or a datum target symbol.

Datum Feature Simulator

(Theoretical)

The theoretically perfect boundary used to establish a datum from a specified datum feature.

Datum Feature Simulator

(Physical)

The physical boundary used to establish a simulated datum from a specified datum feature.

Datum Reference Frame

 Three mutually perpendicular intersecting datum planes.

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.

Datum Target

The designated points, lines or areas that are used in establishing a datum. Datum targets are used in establishing a datum reference frame.

Diameter, Average

The average of several diametric measurements across a circular or cylindrical feature.

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.

Dimension, Basic

A theoretically exact dimension.

Dimension, Reference

A dimension, usually without a tolerance, that is used for informational purposes only. 

Envelope, Actual Mating

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. This envelope is outside the material.

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).

Related Actual Mating Envelope

A similar perfect feature(s) 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).

Envelope, Actual Minimum 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. This envelope is within the material.

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.

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).

Feature

A physical portion of a part such as a surface, pin, hole, slot or its representation on drawings, models or digital data files.

Feature Axis

The axis of the unrelated actual mating envelope of a feature.

Feature, Center Plane of

The center plane of the unrelated actual mating envelope.

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.

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.

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.

Irregular Feature of Size

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.

Feature Control Frame

A rectangle divided into compartments containing the geometric characteristic symbol followed by the tolerance value or description, modifiers and any applicable datum feature references.

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.

Free State

That condition of a part free of applied forces.

Free-State Variation

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.

Flatness

That condition of a surface or derived median plane having all elements in one plane.

Least Material Condition (LMC)

That 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).

Maximum Material Condition (MMC)

That 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).

Non-Uniform Tolerance Zone

A maximum material boundary and a least material boundary, of unique shape, that encompasses the true profile.

Parallelism

That 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.

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:

(a)  nX

(b)  n COAXIAL HOLES

(c)  ALL OVER

(d), A <--> B

(e)  n SURFACES

(f)   Simultaneous Requirement(s)

(g)  INDICATED

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.

Perpendicularity

That condition of a surface, feature's center plane or feature's axis at a right angle to a datum plane or datum axis.

Plane, Tangent

A plane that contacts the high points of the specified feature surface.

Position

The location of one or more features of size relative to one another or to one or more datums. A positional tolerance defines either of the following:

(a) a zone within which the center, axis, or center plane of a feature of size is permitted to vary from a true theoretically exact) position.

(b) (where specified on an MMC or LMC basis) a boundary, defined as the virtual condition, located at the true (theoretically exact) position, that may not be violated by the surface or surfaces of the considered feature of size.

Profile

An outline of a surface, a shape made up of one or more features or a two-dimensional element of one or more features.

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.

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).

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.

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.

Runout

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.

Simultaneous Requirement

Where two or more geometric tolerances apply as a single pattern or part requirement.

Size, Actual Local

The measured value of any individual distance at any cross section of a feature of size.

Size, Limits of

The extent within which variations of geometric form, as well as size, are allowed.

Size, Nominal

The designation used for purposes of general identification.

Straightness

That condition where an element of a surface or derived median line is a straight line. A straightness tolerance specifies a tolerance zone within which the considered element of a surface or derived median line must lie.

Statistical Tolerancing

The assignment 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).

Symmetry

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.

Tolerance

The total amount a specific dimension is permitted to vary. The tolerance is the difference between the maximum and minimum limits.

Tolerance, Bilateral

A tolerance in which variation is permitted in both directions from the specified dimension.

Tolerance, Geometric

The general term applied to the category of tolerances used to control size, form, profile, orientation, location and runout.

Tolerance, Unilateral

A tolerance in which variation is permitted in one direction from the specified dimension.

True Position

The theoretically exact location of a feature.

True Profile

A profile defined by basic radii, basic angular dimensions, basic coordinate dimensions, basic size dimensions, undimensioned drawings, formulas or mathematical data, including design models.

Uniform Tolerance Zone

The distance between two boundaries equally or unequally disposed about the true profile or entirely disposed on one side of the true profile.

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.