angle plate

A precise measurement device used to establish an accurate 90° vertical surface.

angularity

A three-dimensional geometric tolerance that controls how much a surface, axis, or plane can deviate from the angle described in the design specifications.

ASME

The American Society of Mechanical Engineers. ASME is an organization that publishes technical materials and sets industrial and manufacturing standards.

bonus tolerance

Additional tolerance that applies to a feature as its size shifts from a stated material condition. Both MMC and LMC allow bonus tolerance.

circular runout

A two-dimensional geometric tolerance that controls the form, orientation, and location of multiple cross sections of a cylindrical part as it rotates.

circularity

A two-dimensional geometric tolerance that controls how much a feature can deviate from a perfect circle.

concentric

Sharing the same center.

concentricity

A three-dimensional geometric tolerance that controls how much the median points of multiple diameters may deviate from the specified datum axis.

coordinate tolerancing

A system for describing the design of a part that compares its features to distances along three linear axes. These axes create an imaginary rectangular grid.

cross section

A section of a feature that is formed by an intersecting imaginary plane.

cylindricity

A three-dimensional geometric tolerance that controls how much a feature can deviate from a perfect cylinder.

datum

An imaginary, perfect geometric shape or form. A perfect point, line, flat plane, circle, or cylinder are all examples of possible datums.

datum feature

A physical feature that acts as an acceptable substitute for a datum. Datum features relate the various features of the part to each other.

datum reference frame

Three imaginary planes perpendicular to one another that are mapped onto the part to relate features to each other.

feature

A physical feature of a part that naturally contains variation and imperfections. A corner, edge, flat surface, or hole are all examples of possible features.

feature control frame

A series of compartments containing symbols and values that describe the tolerance of a feature. The order and purpose of these compartments follow a consistent standard.

fixture

A dedicated workholding device used to locate and hold a part during machining or inspection.

flatness

A three-dimensional geometric tolerance that controls how much a feature can deviate from a flat plane.

form tolerance

A group of geometric tolerances that limit the amount of error in the shape of a feature. Form tolerances are independent tolerances.

functional gage

A gage for a specific part that quickly checks its form and fit in a manner similar to its intended use.

geometric dimensioning and tolerancing

An international standard for communicating instructions about the design and manufacturing of parts. GD&T uses universal symbols and emphasizes the function of the part.

granite surface plate

A precise, flat plate made of granite that is used to establish a datum plane for inspection. Granite surface plates are available in standardized grades.

individual tolerance

A tolerance that does not require a specified datum.

ISO

The International Organization for Standardization. ISO is an organization based in Switzerland that develops and publishes standards for its international membership base.

least material condition

The point at which a feature contains the least amount of material within its acceptable size limit. The largest acceptable hole and the smallest acceptable shaft are examples of LMC.

location tolerance

A group of geometric tolerances that limit the location or placement of features. Location tolerances are related tolerances.

material condition modifier

One of three modifiers that further define the tolerance of a feature in relation to its acceptable size limits.

maximum material condition

The point at which a feature contains the greatest amount of material within its acceptable size limit. The smallest acceptable hole and the largest acceptable shaft are examples of MMC.

median point

A point that is exactly the same distance between two outer points.

orientation tolerance

A group of geometric tolerances that limit the direction, or orientation, of a feature in relation to other features. Orientation tolerances are related tolerances.

parallelism

A three-dimensional geometric tolerance that controls how much a surface, axis, or plane can deviate from an orientation parallel to the specified datum.

perpendicularity

A three-dimensional geometric tolerance that controls how much a surface, axis, or plane can deviate from a 90 degree angle.

position

A three-dimensional geometric tolerance that controls how much the location of a feature can deviate from its true position.

primary datum

The datum feature that first situates the part within the datum reference frame. The primary datum is the first feature to contact a fixture or surface during assembly.

profile

The outline of a part feature within a given plane.

profile of a line

A two-dimensional geometric tolerance that controls how much the outline of a feature can deviate from the true profile.

profile of a surface

A three-dimensional geometric tolerance that controls how much a surface can deviate from the true profile.

profile tolerance

A group of powerful geometric tolerances that control the size, location, orientation, and form of a feature. Profile tolerances can be either independent or related.

regardless of feature size

A modifier indicating that the stated tolerance for a feature applies regardless of its actual size within an acceptable size limit. RFS does not permit bonus tolerance.

related tolerance

A tolerance that requires a specified datum.

roundness measuring machine

A sophisticated inspection device with a precision spindle that measures various circular or cylindrical features.

runout tolerance

A group of geometric tolerances that simultaneously limit the form, location, and orientation of cylindrical parts. Runout tolerances are related tolerances requiring a datum axis.

secondary datum

The datum feature that situates the part within the datum reference frame after the primary datum. The secondary datum is the second feature to contact a fixture or surface during assembly.

straightness

A two-dimensional geometric tolerance that controls how much a feature can deviate from a straight line.

symmetry

A three-dimensional geometric tolerance that controls how much the median points between two features may deviate from a specified axis or center plane.

tertiary datum

The datum feature that situates the part within the datum reference frame after the secondary datum.

three-dimensional tolerance

A tolerance that controls a shape having a length, width, and depth.

tolerance

An unwanted but acceptable deviation from a given dimension. Tolerances indicate the allowable difference between a physical feature and its intended design.

tolerance zone

An imaginary zone in which a part feature must be completely contained for the part to pass inspection.

total runout

A three-dimensional geometric tolerance that controls the form, orientation, and location of the entire length of a cylindrical part as it rotates.

true position

The imaginary perfect position of a feature described by the design specifications.

true profile

The perfect, imaginary profile described by the design specifications.

two-dimensional tolerance

A tolerance that controls a shape having only a length and width.