GD&T Definitions

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.

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.

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.

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

The theoretically perfect boundry (virtual condition or actual mating envelope) or best-fit (tangent) plane of a specified datum feature.

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.

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.

A point, axis, ot plane established by processing or inspection equipment, such as the following simulators: surface plate, a gage surface, or mandrel.

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

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.

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.

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.

A general term appiled to a physical portion of a part, such as a surface, pin, tab, hole, or slot.

A straight line that coincides with the axis of the true geometric counterpart of the specified feature.

A plane that coincides with the center plane of the true geometric counterpart of the specified feature.