Definitions

The following terms are defined as their use applies in this Standard. Additionally, definitions throughout the Standard of italicized terms are given in sections describing their application. Their location may be identified by referring to the index.

1.3.1 Boundary, Innar. A worst case boundary (that is, locus) 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) from the feature's departure from its specified material condition. See Figs. 2-9 through 2-12.

1.3.2 Boundary, Outer. A worst case boundary (that is, locus) generated by the largest feature (LMC for an internal feature and MMC for an external feature) plus the geometric tolerance and any additional geometric tolerance (if applicable) from the feature's

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departure from its specified material condition. See Figs. 2-9 through 2-12.

1.3.3 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.

1.3.4 Datum Feature. An actual feature of a part that is used to establish a datum.

1.3.5 Datum Fsature Simulator. A surface of adequately precise form (such as a surface plate, a gage surface, or a mandrel) contacting the datum feature(s) and used to establish the simulated datum(s).

NOTE: Simulated datum features are used as the practical embodiment of the datums during manufacture and inspection.

1.3.6 Datum, Simulated. A point, axis, or plane established by processing or inspection equipment, such as the following simulators: a surface plate, a gage surface, or a mandrel. See paras. 4.4.1 and 4.4.2.

1.3.7 Datum Target. A specified point, line, or area on a part used to establish a datum.

1.3.8 Dimension. A numerical value expressed in appropriate units of measure and used to define the size, location, geometric characteristic, or surface texture of a part or part feature.

1.3.9 Dimension, Basic. A numerical value used to describe the theoretically exact size, profile, orientation, or location of a feature or datum target. See Fig. 3-7. It is the basis from which permissible variations are established by tolerances on other dimensions, in notes, or in feature control frames. See Figs. 2-14, 2-15, and 3-25.

1.3.10 Dimension, Reference. A dimension, usually without tolerance, used for information purposes only. A reference dimension is a repeat of a dimension or is derived from other values shown on the drawing or on related drawings. It is considered auxiliary information and does not govern production or inspection operations. See Figs. 1-17 and 1-18.

1.3.11 Envelope, Actual Mating. This term is defined according to the type of feature, as follows:

(a) For an External Feature. A similar perfect feature counterpart of smallest size that can be circumscribed about the feature so that it just contacts the surface at the highest points. For example, a smallest cylinder of perfect form or two parallel planes of perfect form at minimum separation that 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), for example, perpendicular to a primary datum plane.

(b) For an Internal Feature. A similar perfect feature counterpart of largest size that can be inscribed within the feature so that it just contacts the surface at the highest points. For example, a largest cylinder of perfect form or two parallel planes of perfect form at maximum separation that 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).

1.3.12 Feature. The general term applied to a physical portion of a part, such as a surface, pin. tab. hole, or slot.

1.3.13 Feature, Axis Of. A straight line that coincides with the axis of the true geometric counterpart of the specified feature.

1.3.14 Feature, Center Plane Of. A plane that coincides with the center plane of the true geometric counterpart of the specified feature.

1.3.15 Feature, Derived Median Plane Of. An imperfect plane (abstract) that passes through the center points of all line segments bounded by the feature. These line segments are normal to the actual mating envelope.

1.3.16 Feature, Derived Median Line Of. An imperfect line (abstract) that passes through the center points of all cross sections of the feature. These cross sections are normal to the axis of the actual mating envelope. The cross section center points are determined as per ANSI B89.3.1.

1.3.17 Feature of Size. One cylindrical or spherical surface, or a set of two opposed elements or opposed parallel surfaces, associated with a size dimension.

1.3.18 Full Indicator Movement (FIM). The total movement of an indicator where appropriately applied to a surface to measure its variations.

1.3.19 Least Material Condition (LMC). The condition in which a feature of size contains the least amount of material within the stated limits of size — for example, maximum hole diameter, minimum shaft diameter.

1.3.20 Maximum Material Condition (MMC).

The condition in which a feature of size contains the maximum amount of material within the stated limits of size — for example, minimum hole diameter, maximum shaft diameter.

1.3.21 Plane, Tangent. A theoretically exact plane derived from the true geometric counterpart of the specified feature surface.

1.3.22 Regardless of Feature Size (RFS). The term used to indicate that a geometric tolerance or datum reference applies at any increment of size of the feature within its size tolerance.

1.3.23 Resultant Condition. The variable boundary generated by the collective effects of a size feature's specified MMC or LMC material condition, 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. 2-9 through 2-12.

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

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

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

1.3.27 Size, Limits Of. The specified maximum and minimum sizes. See para. 2.7.

1.3.28 Size, Nominal. The designation used for purposes of general identification.

1.3.29 Size, Resultant Condition. The actual value of the resultant condition boundary.

1.3.30 Size, Virtual Condition. The actual value of the virtual condition boundary.

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

1.3.32 Tolerance, Bilateral. A tolerance in which variation is permitted in both directions from the specified dimension.

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

1.3.34 Tolerance, Unilateral. A tolerance in which variation is permitted in one direction from the specified dimension.

1.3.35 True Geometric Counterpart. The theoretically perfect boundary (virtual condition or actual mating envelope) or best-fit (tangent) plane of a specified datum feature. See Figs. 4-11 and 4-10. Aiso see paras. 1.3.5 and 1.3.6 regarding the simulated datum.

1.3.36 True Position. The theoretically exact location of a feature established by basic dimensions.

1.3.37 Virtual Condition. A constant boundary generated by the collective effects of a size feature's specified MMC or LMC material condition and the geometric tolerance for that material condition. See Figs. 2-9 through 2-12.

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