Term
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Definition
| A worst case boundry (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 goemetric tolerance (if applicable) from the features departure from its specified material condition. |
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Term
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Definition
| A worst case boundry (that is, locus) generated by the largest feature (LMC for an internal feature and MMC for an external feature) plus the stated geometric tolerance and any additional goemetric tolerance (if applicable) from the features departure from its specified material condition. |
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Term
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Definition
| 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. |
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Term
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Definition
| An actual feature of a part that is used to establish a datum. |
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Term
| True Geometric Counterpart |
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Definition
| The theoretically perfect boundry (virtual condition or actual mating envelope) or best-fit (tangent) plane of a specified datum feature. |
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Term
| Datum features subject to size variation |
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Definition
| Datum features, such as diameters and widths, differ from singular flat features in that they are subject to variations in size as well as form. |
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Term
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Definition
| A surface of adequately precise form (such as a surface plate, a gage surface, or mandrel) contacting the datum feature(s) and used to establish the simulated datums. |
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Term
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Definition
| A point, axis, ot plane established by processing or inspection equipment, such as the following simulators: surface plate, a gage surface, or mandrel. |
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Term
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Definition
| A specified point, line, or area on a part used to establish a datum. |
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Term
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Definition
| A numerical value expressed in appropriate units of measure and used to define the size, location, and geometric characteristis, or surface texture of a part or part feature. |
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Term
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Definition
| A numerical value used to describe the theoretically exact size, profile, orentation, or location of a feature or a datum tatget. It is the basis from whigh permissible variations are established by tolerances on other dimensions, in notes, or in feature control frames. |
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Term
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Definition
| 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 opertions. |
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Term
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Definition
| A general term appiled to a physical portion of a part, such as a surface, pin, tab, hole, or slot. |
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Term
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Definition
| A straight line that coincides with the axis of the true geometric counterpart of the specified feature. |
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Term
| Center plane of a feature |
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Definition
| A plane that coincides with the center plane of the true geometric counterpart of the specified feature. |
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Term
| Derived median line of a feature |
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Definition
| 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. |
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Term
| Derived median plane of a feature |
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Definition
| An imperfect plane (abstract) that passes through the center points of all line segments of the feature. These line segments are normal to the actual mating envelope. |
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Term
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Definition
| One cylindrical or spherical surface, or a set of two opposed elements or opposed parallel surfaces, associated with a size dimension. |
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Term
| Individual features of size (Rule #1) |
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Definition
| Where only a tolerance of size is specified, the limits of size of an individual feature prescribe the extent to which variations in its geometric form, as well as size, are allowed |
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Term
| Maximum Material Contition (MMC) |
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Definition
| The condition in which a feature of size contains the maximum amount of material within the stated limits if size -- for example, minimum hole diameter, maximum shaft diameter. |
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Term
| Least Material Contition (LMC) |
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Definition
| The condition in which a feature of size contains the least amount of material within the stated limits if size -- for example, maximum hole diameter, minimum shaft diameter. |
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Term
| Regardless of Featue Size (RFS) |
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Definition
| The term used to indicate that a geometric tolerance or datum reference applies at any increment of size of the feature within its tolerance. |
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Term
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Definition
| The variable boundry 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. |
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Term
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Definition
| A constant boundry generated by the collective effects of a size feature's specified MMC or LMC material condition and the geometric tolerance for that material condition. |
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Term
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Definition
| The general term for the size of a produced feature. This term includes the actual mating size and the actual local sizes. |
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Term
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Definition
| The value of any indiviual distance at any cross section of a feature. |
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Term
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Definition
| The dimensional value of the actual mating envelope. |
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Term
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Definition
This term is defined according to the type of feature, as follows"
a) For an external feature. A similar perfect 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).
b) For an internal feature. A similar perfect 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 controled 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. |
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Term
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Definition
| The specified maximum and minimum sizes. |
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Term
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Definition
| The designation used for purposes of general identification. |
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Term
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Definition
| The actual value of a resultant contition boundry. |
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Term
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Definition
| The dimensional value of a virtual contition boundry. |
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Term
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Definition
| A theoretically exact plane derived from the true geometric counterpart of the specified feature surface. |
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Term
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Definition
| The total amount a specific dimension is permitted to vary. The tolerance is the difference between the maximum and minimum limits. |
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Term
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Definition
| A tolerance in which variation is permitted in both directions from the specified dimension. |
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Term
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Definition
| The general term applied to the category of tolerances used to control form, profile, orientation, location, and runout. |
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Term
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Definition
| _____ tolerances control straightness, flatness, circularity, and cylindricity. |
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Term
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Definition
| _______ is the condition of a surface having all elements in one plane. |
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