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. |