Angularity

A threedimensional orientation tolerance that describes the allowable variability in the angular relationship between a surface and a datum. Angularity is a related tolerance.

ASME

American Society of Mechanical Engineers. ASME is an organization that publishes technical materials and sets industrial and manufacturing standards. Along with ISO, ASME provides written standarization for GD&T in ASME Y14.5M.

Basic Dimension

A dimension that is theoretically perfect. A basic dimension has no direct tolerance and is denoted on a GD&T blueprint as a number enclosed in a rectangular box.

Circular Runout

A twodimensional geometric tolerance that controls the form, orientation, and location of multiple cross sections of a cylindrical part as it rotates. Circular Runout is a related tolerance.

Circularity

A twodimensional form tolerance that describes the allowable variability in the shape and appearance of a circle. Also known as roundness, circularity is an individual tolerance.

Coaxial

Sharing a common center between two cylindrical features. Circularity requires any twodimensional cross section of a feature to remain within two imaginary coaxial circles.

Concentricity

A threedimensional locational tolerance that describes the location of opposing points in cylindrical features with respect to a datum reference. Concentricity is a related tolerance.

Controlled Radius

A radius that yields a circle, arc, or sphere with no flat sections or reversals. In GD&T, controlled radius occurs on a blueprint with the symbol CR.

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. Circularity requires any twodimensional cross section of a feature to remain within two imaginary concentric circles.

Cylindricity

A threedimensional form tolerance that describes the allowable variability in the shape and appearance of a cylinder. Cylindricity is an individual tolerance.

Datum

A point of reference for machine tools, programs, and fixtures from which measurements are taken. A datum can be a hole, line, or any threedimensional shape.

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.

Diameter

The distance from one edge of a circle to the opposite edge that passes through the center. Round or cylindrical features require diameter measurements.

Feature Control Frame

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

Flatness

A threedimensional form tolerance that describes the allowable variability in the shape and appearance of a surface that lies in a plane. Flatness is an individual tolerance.

Form Tolerance

A geometric tolerance that limits the amount of error in the shape of a feature. The form tolerances include straightness, flatness, circularity, and cylindricity.

Functional Gage

A gage representing a "worst case" mating part that provides a simple pass/fail assessment of the inspected part. Functional gages can quickly inspect several features at once.

Geometric Dimensioning and Tolerancing

GD&T. 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.

Individual Tolerance

A tolerance that does not require a specified datum. Form tolerances are always individual tolerances, while profile tolerances can sometimes be individual tolerances.

ISO

The International Organization for Standardization. ISO establishes documented standards, rules, and guidelines to ensure that products, processes, and services are fit for their purpose. Along with ASME, ISO provides written standarization for GD&T in ISO 1101.

Least Material Condition

LMC. 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 geometric tolerance that limits the location or placement of features. Location tolerances are related tolerances.

Material Condition Modifier

Defines the tolerance of a feature in relation to its acceptable size limits. There are three material condition modifiers in GD&T: maximum material condition, least material condition, and regardless of feature size.

Maximum Material Condition

MMC. 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. Concentricity finds the median point between two points opposite each other forming a diameter on a cylindrical feature.

Modifier

Elements that communicate information about the tolerance of a feature. In GD&T, each modifier has a symbol that distinguishes it with other modfiers on a blueprint.

Orientation Tolerance

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

Parallelism

A threedimensional orientation tolerance that describes the equal distance between pairs of points, lines, or planes. Parallelism is a related tolerance.

Perpendicularity

A threedimensional orientation tolerance that describes the allowable variability in the 90° angular relationship between a surface and a datum. Perpendicularity is a related tolerance.

Position

A threedimensional geometric tolerance that controls how much the location of a feature can deviate from its true position. Position is a related tolerance.

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 the part feature within a given plane. Twodimensional profiles are toleranced using profile of a line, and threedimensional profiles are toleranced using profile of a surface.

Profile of a Line

A twodimensional profile tolerance that describes the allowable variability in the contour of the edge seen in the section view. Profile of a line can be either an individual or a related tolerance.

Profile of a Surface

A threedimensional profile tolerance that describes the allowable variability in the contour of a surface. Profile of a surface can be either an individual or a related tolerance.

Profile Tolerance

A geometric tolerance that controls the size, location, orientation, and form of a feature. Profile tolerances can be either individual or related.

Projected Tolerance Zone

A tolerance zone that extends beyond a feature by a specified distance. Symbolized by a "P" enclosed in a circle, projected tolerance zones help ensure that mating parts fit during assembly.

Radius

The distance from a center point to a point on a circle or arc. In GD&T, radius forms a curved feature formed by identifying a uniform distance from a center point to the edge of a circle or an arc.

Reference Dimension

A dimension that is provided for informational purposes only. A feature is on a GD&T blueprint for reference, rather than for inspection or production use, if its dimensions are enclosed in parentheses.

Regardless of Feature Size

RFS. 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. Orientation, location, and runout are always related tolerances.

Roundness Machine

A sophisticated inspection device with a precision spindle that measures various circular and cylindrical features. It is necessary for inspecting such tolerances as circularity, cylindricity, circular runout, and total runout.

Runout Tolerance

A geometric tolerance that simultaneously limits 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 twodimensional form tolerance that describes allowable variability in the shape and appearance of a line in a section view. Straightness is an individual tolerance.

Symmetry

A threedimensional geometric tolerance that controls how much the median points between two features may deviate from a specified axis or center plane. Symmetry is a locational tolerance.

Tangent Plane

A modifier specifying that the tolerance zone applies to a plane defined by the high points on a surface. In GD&T, tangent plane is symbolized by a capital T enclosed in a circle.

Tertiary Datum

The datum feature that situates the part within the datum reference frame after the secondary datum. This plane must be perpendicular to both the primary and secondary planes and is usually the smallest surface of the workpiece.

ThreeDimensional Tolerance

A tolerance that controls a shape having a length, width, and depth. Flatness, profile of a surface, and angularity are all examples of threedimensional tolerances.

Tolerance Zone

An imaginary zone in which a part feature must be completely contained for the part to pass inspection. This zone contains the dimensions between the maximum and minimum limits of a feature's location.

Total Runout

A threedimensional geometric tolerance that controls the form, orientation, and location of the entire length of a cylindrical part as it rotates. Total runout is a related tolerance.

True Position

The imaginary perfect position of a feature described by the design specifications. The location of a feature's true position is determined by the positional tolerance.

True Profile

The perfect, imaginary profile described by the design specifications. The profile tolerances compare the actual profile of a feature to the true profile.

TwoDimensional Tolerance

A tolerance that controls a shape having only a length and width. Straightness, Circularity and circular runout are all examples of twodimensional tolerances.

Unequal Tolerance Zone

A tolerance zone used for the profile tolerances that designates if a given tolerance is not equally disposed around the true profile. A profile may be unequal on two sides or one side.
