What is the definition of "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. Symmetry is a locational tolerance.

## Inspection Training

Class Information
 Tooling U-SME classes are offered at the beginner, intermediate, and advanced levels. The typical class consists of 12 to 25 lessons and will take approximately one hour to complete.
 Class Name: Intro to GD&T 205 (2009) Description: This class introduces the fundamental concepts of geometric dimensioning and tolerancing (GD&T) and describes the main types of tolerances included in the standard, ASME Y14.5 2009.Includes an Interactive Lab. Difficulty: Intermediate Number of Lessons: 18 Language: English

Class Outline
• Objectives
• What is GD&T?
• Datums and Features
• The Feature Control Frame
• Material Condition Modifiers
• Modifier Symbols
• Basic and Reference Dimensions
• GD&T vs. Coordinate Tolerancing
• Types of Tolerances
• Straightness and Flatness
• Circularity vs. Cylindricity
• Profile of a Line and Surface
• Angularity, Perpendicularity, and Parallelism
• Position
• Concentricity and Symmetry
• Circular and Total Runout
• Summary

Class Objectives
• Define GD&T.
• Distinguish between a datum and a feature.
• List the contents of the feature control frame.
• List the material condition modifiers.
• List the GD&T modifiers not dealing with material condition.
• Identify basic and reference dimensions and explain their purpose.
• Distinguish between traditional tolerancing and GD&T.
• List the major categories of geometric tolerances.
• Describe the straightness tolerance and the flatness tolerance.
• Describe the circularity tolerance and the cylindricity tolerance.
• Describe the profile of a line tolerance and the profile of a surface tolerance.
• Describe the angularity, perpendicularity, and parallelism tolerances.
• Describe the position tolerance.
• Describe the concentricity and symmetry tolerance.
• Describe the circular runout tolerance and the total runout tolerance.
• Describe the advantages of GD&T.

Class Vocabulary

Vocabulary TermDefinition
A three-dimensional orientation tolerance that describes the allowable variability in the angular relationship between a surface and a datum. Angularity is a related tolerance.
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.
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.
A two-dimensional 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.
A two-dimensional form tolerance that describes the allowable variability in the shape and appearance of a circle. Also known as roundness, circularity is an individual tolerance.
Sharing a common center between two cylindrical features. Circularity requires any two-dimensional cross section of a feature to remain within two imaginary coaxial circles.
A three-dimensional locational tolerance that describes the location of opposing points in cylindrical features with respect to a datum reference. Concentricity is a related tolerance.
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.
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.
A section of a feature that is formed by an intersecting imaginary plane. Circularity requires any two-dimensional cross section of a feature to remain within two imaginary concentric circles.
A three-dimensional form tolerance that describes the allowable variability in the shape and appearance of a cylinder. Cylindricity is an individual tolerance.
A point of reference for machine tools, programs, and fixtures from which measurements are taken. A datum can be a hole, line, or any three-dimensional shape.
A physical feature that acts as an acceptable substitute for a datum. Datum features relate the various features of the part to each other.
The distance from one edge of a circle to the opposite edge that passes through the center. Round or cylindrical features require diameter measurements.
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.
A three-dimensional 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.
A geometric tolerance that limits the amount of error in the shape of a feature. The form tolerances include straightness, flatness, circularity, and cylindricity.
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.
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.
A tolerance that does not require a specified datum. Form tolerances are always individual tolerances, while profile tolerances can sometimes be individual tolerances.
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.
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.
A geometric tolerance that limits the location or placement of features. Location tolerances are related tolerances.
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.
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.
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.
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.
A geometric tolerance that limits the direction, or orientation, of a feature in relation to other features. Orientation tolerances are related tolerances.
A three-dimensional orientation tolerance that describes the equal distance between pairs of points, lines, or planes. Parallelism is a related tolerance.
A three-dimensional orientation tolerance that describes the allowable variability in the 90° angular relationship between a surface and a datum. Perpendicularity is a related tolerance.
A three-dimensional geometric tolerance that controls how much the location of a feature can deviate from its true position. Position is a related tolerance.
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.
The outline of the part feature within a given plane. Two-dimensional profiles are toleranced using profile of a line, and three-dimensional profiles are toleranced using profile of a surface.
A two-dimensional 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.
A three-dimensional 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.
A geometric tolerance that controls the size, location, orientation, and form of a feature. Profile tolerances can be either individual or related.
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.
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.
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.
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.
A tolerance that requires a specified datum. Orientation, location, and runout are always related tolerances.
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.
A geometric tolerance that simultaneously limits the form, location, and orientation of cylindrical parts. Runout tolerances are related tolerances requiring a datum axis.
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.
A two-dimensional form tolerance that describes allowable variability in the shape and appearance of a line in a section view. Straightness is an individual tolerance.
A three-dimensional 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.
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.
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.
A tolerance that controls a shape having a length, width, and depth. Flatness, profile of a surface, and angularity are all examples of three-dimensional tolerances.
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.
A three-dimensional 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.
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.
The perfect, imaginary profile described by the design specifications. The profile tolerances compare the actual profile of a feature to the true profile.
A tolerance that controls a shape having only a length and width. Straightness, Circularity and circular runout are all examples of two-dimensional tolerances.
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.