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GD&T Glossary

(Based on ASME Y14.5-2009)

GD&T (geometric dimensioning and tolerancing) is an international language that is used on engineering drawings to accurately describe the size, form, orientation, and location of part features. It is also a design-dimensioning philosophy that encourages designers to define a part based on how it functions in the final product or assembly.

GD&T is an exact language that enables design engineers to "say what they mean" on a drawing, thus improving product designs and lowering cost. Process engineers and manufacturing use the language to interpret the design intent and to determine the best manufacturing approach. Quality control and inspection use the GD&T language to determine proper set-up and part verification.

By providing company-wide uniformity in the drawing specifications and interpretation, GD&T reduces controversy, guesswork, and assumptions throughout the design, manufacturing and inspection process.

Understanding how to apply and interpret GD&T correctly will help you:

  • Create clear, concise drawings
  • Improve product design
  • Create drawings that reduce controversy, guesswork, and assumptions throughout the manufacturing process
  • Effectively communicate or interpret design requirements for suppliers and manufacturing

However, because GD&T is such a precise language, it involves a great many symbols and terms. Here is a list of some of the topics involved in geometric dimensioning and tolerancing fundamentals and a short definition of each.


The following terms are related to GD&T. Unless otherwise noted, the definition is from ASME Y14.5M-2009.

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Actual Local Size - The measured value of any individual distance at any cross section of a feature of size.

Actual Mating Envelope - This envelope is outside the material. A similar perfect feature(s) counterpart of smallest size that can be contracted about an external feature(s) or largest size that can be expanded within an internal feature(s) so that it coincides with the surface(s) at the highest points. There are two types of actual mating envelopes: related and unrelated.

Actual Minimum Material Envelope - This envelope is within the material. A similar perfect feature(s) counterpart of largest size that can be expanded within an external feature(s) or smallest size that can be contracted about an internal feature(s) so that it coincides with the surface(s) at the lowest points. There are two types of actual mating envelopes: unrelated and related.
all around symbol All-Around Symbol - The symbolic means of indicating that a tolerance applies to surfaces all around the part is a circle located at the junction of a leader from the feature control frame.

All-Over Symbol - The symbolic means of indicating that a profile tolerance zone applies to all surfaces, all over the three-dimensional profile of a part.

angularity symbol Angularity - The condition of a surface, feature’s center plane, or feature’s axis at any specified angle from a datum plane or datum axis.

Angularity Tolerance - A geometric tolerance that limits the amount a surface, axis, or center plane is permitted to deviate from a basic angle relative to a datum reference frame.

Annotation - Dimensions, tolerances, notes, text, or symbols visible without any manual or external manipulation.

Annotation Plane - A conceptual plane containing annotation that either perpendicularly intersects or is coincident with one or more surfaces of a feature.

Arc - A segment of a curve.

ASME Y14.41-2012 - American Society of Mechanical Engineers Standard on Digital Product Definition Data Practices.

ASME Y14.5-2009 - The national standard for dimensioning and tolerancing in the United States. ASME stands for American Society of Mechanical Engineers. The Y14.5 is the standard number, and 2009 is the date the standard was officially approved.

ASME Y14.5M-1994 - The national standard for dimensioning and tolerancing in the United States. ASME stands for American Society of Mechanical Engineers. The Y14.5 is the standard number. "M" is to indicate the standard is metric, and 1994 is the date the standard was officially approved.

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Assembly - A number of parts, or combination thereof, that are joined together to perform a specific function and subject to disassembly without degradation of any of the parts (e.g., power shovel-front, fan assembly, audio frequency amplifier).

Assembly Model - A model in which the product described is an assembly of two or more items.

Associated Entities - The portion of a product definition to which annotation applies.

Associated Group - A user defined set of related digital elements.

Associativity - The established relationship between digital elements.

Attribute - A dimension, tolerance, note, text, or symbol required to complete the product definition or feature of the product that is not visible but available upon interrogating the model.

Attribute Data - Information obtained from an inspection process that indicates only whether a part is acceptable or not acceptable.

Attribute Gage - The family of receiver gages used to collect attributes data; for example, GO and functional gages.

Average Diameter - The average of several diametric measurements across a circular or cylindrical feature.

AVG - Placed near the qualified size dimension where a form control (such as circularity) is specified in a free state. It is then used to ensure that the actual diameter of the feature can be restrained to the desired shape at assembly.

Axis - A theoretical straight line about which a geometric object rotates or may be imagined to rotate. Where the term “axis” is used in this text, unless otherwise indicated, it refers to the axis of the unrelated actual mating envelope of a cylindrical feature of size.

Axis/Center Plane Interpretation - A straight line that coincides with the axis of the true geometric counterpart of the specified feature.

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

Axis Offset - The parallel distance between two axes; for example, the distance between a part feature of size axis and a datum axis.

Axis Theory - When the axis (or center plane) of the feature of size must be within the tolerance zone.

Basic Angle - A type of basic dimension with an angular value used to define the orientation of a part feature or datum target.
basic dimension Basic Dimension - The axis (or center plane) of the unrelated actual mating envelope of the feature of size must be within the tolerance zone.
between Between Symbol - The axis (or center plane) of the unrelated actual mating envelope of the feature of size must be within the tolerance zone.

Bidirectional Position Tolerance - Bidirectional Position Tolerance.

Bilateral Equally Disposed Tolerance Zone - A tolerance zone that is equally divided bilaterally to both sides of the true profile.

Bilateral Unequally Disposed Tolerance Zone - An unequally disposed tolerance zone is indicated with an unequally disposed profile symbol in the feature control frame following the tolerance value. A second value after the symbol indicates the tolerance in the direction that adds material to the true profile.

Bilateral Tolerance - A type of plus-minus tolerance that allows a dimension to vary in both the plus and minus directions.

Bilateral Tolerance Zone - A tolerance zone that is divided bilaterally to both sides of the true profile.

Bonus Tolerance - A potential additional tolerance for a geometric tolerance.

Boundary - A keyword used with a position tolerance on to denote that only a boundary interpretation exists for the position tolerance. There is no axis interpretation.

"By" Symbol - A symbol that indicates a relationship between two coordinate dimensions.

Cartoon Gage - A simplified sketch of a functional gage.

Center Plane - A theoretical plane about which a geometric object is equally disposed. Where the term “center plane” is used, unless otherwise indicated, it refers to the center plane of the unrelated actual mating envelope of a width feature of size.

Circular Runout Tolerance - A geometric tolerance that limits the high to low point deviation (runout) of the circular elements of any surface of revolution or the circular elements of a planar surface that is perpendicular to and intersects the datum axis. The tolerance zone (runout) applies independently at each circular element of the toleranced surface (i.e., at each cross section perpendicular to the datum axis).
circularity Circularity - The condition of a surface where: a) For a feature other than a sphere (e.g., cylinder, cone, etc.), all points of the surface intersected by any plane perpendicular to an axis or spine (curved line) are equidistant from that axis or spine (curved line). b) For a sphere, all points of the surface intersected by any plane passing through a common center are equidistant from that center.

Circularity Tolerance - A geometric tolerance that limits the circularity deviation (radial deviation between highest and lowest points) on individual circular elements.

Coaxial Datum Features - Coaxial diameters used to create a single datum axis.

Coaxial Diameters - Two (or more) diameters that are shown on the drawing as being on the same center line (axis).

Coaxiality - The condition where the axes of the unrelated actual mating envelopes, axis of the unrelated minimum material envelope, or median points (as applicable) of one or more surfaces of revolution are coincident.

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Commercial and Government Entity (CAGE) Code - A five character code that provides a unique activity identifier used by the government for activity identification.

Composite Position Tolerancing - A multiple-segment feature control frame with one position symbol.

Complex Feature - A single surface of compound curvature or a collection of other features that constrains up to six degrees of freedom.

Composite Position Tolerance - A single surface of compound curvature or a collection of other features that constrains up to six degrees of freedom.

Composite Profile Tolerance - A feature control frame that contains multiple segments with a single entry of a position tolerance that is applicable to all horizontal segments of the feature control frame.
concentricity Concentricity - The condition where the median points of all diametrically opposed elements of a surface of revolution (or the median points of correspondingly located elements of two or more radially disposed features) are congruent with the datum axis (or center point).

Concentricity Tolerance - A geometric tolerance that defines the permissible deviation that all median points of a surface of revolution (or correspondingly located elements of two or more radially disposed features) are permitted to vary from a datum axis or center point.

Conical - A surface of revolution that has a taper symmetrical about its axis. See conical taper.

Conical Taper - The ratio of the difference in the diameters of two sections (perpendicular to the axis) of a cone to the distance between these sections. See ASME Y14.5-2009 paragraph 2.13 for acceptable methods of dimensioning.

Conicity - A profile tolerance applied to a conical surface to control form, or combination of size, form, orientation, and location.

Constraint - A limit to one or more degrees of freedom.

Continuous Feature Symbol - A symbol that indicates where a group of two or more features of size are to be treated geometrically as a single feature or feature of size.
controlled radius Controlled Radius - A radius where the part surface must have a smooth curve within the tolerance zone. In a controlled radius, no flats or reversals are permitted on the arc surface.

Coordinate Measuring Machine (CMM) - A precision three-axis machine used to collect and analyze surface points from a part to verify the geometric requirements (size, location, orientation, and form) of part features.

Coordinate Tolerancing - A dimensioning system where the coordinates (X,Y,Z) of the centers of features of size and surfaces are located (or defined) by means of linear dimensions with plus-minus tolerances.

Coplanar Datum Features - Two or more planar datum features that are on the same plane.

Coplanarity - The condition of two or more surfaces having all elements in one plane.

Copy - Any reproduction or duplication, in any media, of the original.

Counterbore - A flat-bottomed diameter.

Counterbore Symbol - Symbolic means of indicating a counterbore.

Countersink - An angular lead-in to enlarge and bevel the top of a hole so that a screw, or bolt can be inserted flush with the surface.

Countersink Symbol - Symbolic means of denoting the shape of geometry on a part.
cylindricity Cylindricity - The condition of a surface of revolution in which all points of the surface are equidistant from a common axis. 

Cylindricity Gage - An instrument used to measure cylindricity deviation.

Cylindricity Tolerance - A geometric tolerance that defines the deviation permitted on a cylindrical surface. A cylindricity tolerance applies along the entire cylindrical surface simultaneously.

Data - Information represented in a formal manner suitable for communication, interpretation, or processing by human beings or computers.

Datum - A theoretically exact plane, point or axis from which a dimensional measurement is made. 

Datum Axis - The axis of a datum feature simulator established from the datum feature.

Datum Center Plane - The center plane of a datum feature simulator established from the datum feature.

Datum Center Point - The center point of a datum feature simulator established from the datum feature.
datum feature Datum Feature - A feature or feature of size that is identified with either a datum feature symbol or a datum target symbol.

Datum Feature Reference - The desired order of precedence is indicated by entering the appropriate datum feature reference letter, from left to right, in the feature control frame.

Datum Feature Shift - The allowable movement or looseness between the part datum feature and the datum feature simulator.

Datum Feature Simulator (Physical) - The physical boundary used to establish a simulated datum from a specified datum feature.

Datum Feature Simulator (Theoretical) - The theoretically perfect boundary used to establish a datum from a specified datum feature.

Datum Plane - A datum established from the datum feature simulator of a nominally flat datum feature. It constrains three degrees of freedom (one translation and two rotations).

Datum Reference Frame - A set of three mutually perpendicular datum planes. The datum reference frame provides direction as well as an origin for dimensional measurements.

Datum Reference Frame Symbol - A symbol used to label axes of a datum reference frame. The X, Y, Z labels represent the translational degrees of freedom.

Datum Shift - The allowable movement or looseness between the part datum feature and the datum. The datum feature shift / displacement shall always be limited or constrained by the datum feature simulator.

Datum System - A set of symbols and rules on how to constrain a part to establish a relationship between the part and geometric tolerance zones.
datum target Datum Target - A set of symbols that describe the shape, size, and location of datum feature simulators that are used to establish datum planes, axes, or points.

Datum Target Area - A designated area used in establishing a datum.

Datum Target Identification System - A means of designating a datum target on a drawing. The symbol is paced outside the part outline with a radial line directed to the target.

Datum Target Line - A designated line used in establishing a datum.

Datum Target Point - A designated point used in establishing a datum.

Datum Target Symbol - A circular symbol with a horizontal line dividing the symbol into two halves. The bottom half denotes the datum letter and the target’s number. The top half denotes the datum feature simulator size, when applicable.

Degrees of Freedom (DOF) - The movement of a part in space. A rigid part has six degrees of freedom: three translational degrees of freedom and three rotational degrees of freedom.

Depth - Refers to how deep a feature is on a part.

Depth Symbol - Indicates the depth of a hole, counterbore, or spotface.

Derivative - A symbol that describes the shape, size, and location of gage elements that are used to establish datum planes or axes.

Derived Median Line - An imperfect line formed by the center points of all cross sections of a feature of size.

Derived Median Plane - An imperfect plane formed by the center points of all line segments bounded by the feature of size.

Design Model - A symbol that describes the shape, size, and location of gage elements that are used to establish datum planes or axes.

Dial Indicator - An instrument used to accurately measure small linear distances, frequently used in inspection of parts.

Diameter - The length of a straight line that passes through the center of a circle or cylinder and touches two points on its edge.

Diameter Symbol - A symbol that describes the shape, size, and location of gage elements that are used to establish datum planes or axes.

Die Closure - A symbol that describes the shape, size, and location of gage elements that are used to establish datum planes or axes.

Digital Data - A symbol that describes the shape, size, and location of gage elements that are used to establish datum planes or axes.

Digital Element - A symbol that describes the shape, size, and location of gage elements that are used to establish datum planes or axes.

Dimension - A numerical value(s) or mathematical expression in appropriate units of measure used to define the size, location, orientation, or form (shape) of a feature (i.e., surface) or feature of size.

Draft - A numerical value expressed in appropriate units of measure and used to define the size, location, orientation, form, or other geometric characteristics of a part.

Drawing - An engineering document or digital data file(s) that discloses (either directly or by reference) by means of graphic or textural presentations, or by combinations of both, the physical or functional requirements of an item.

Drawing Format - The arrangement and organization of information within a drawing. This includes such features as the size and arrangement of blocks, notes, lists, and revision information and the use of optional or supplemental blocks.

Elongated Hole - A hole with a different length and width (commonly referred to as a slot).

Engineering Drawing - A document that communicates a precise description of a part. This description consists of pictures, words, numbers, and symbols.

Equal Bilateral Tolerance - Where the allowable variation from the specified dimension (nominal) value is the same in both directions.

Feature - A physical portion of a part, such as a surface, pin, hole, or slot or its representation on a drawing, model, or digital data files.

Feature Axis - The axis of the unrelated actual mating envelope of a feature.

Feature Center Plane - The center plane of the unrelated actual mating envelope of a feature.

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feature control frame Feature Control Frame - A rectangular box that is divided into compartments within which the geometric characteristic symbol, tolerance value, modifiers, and datum references are placed.

Feature of Size - A general term that is used to refer to either a regular feature of size or an irregular feature of size.

First Angle Projection - A dimension that is associated with a feature of size.

Fixed Fastener Assembly - An assembly of two or more parts where a fastener is held in place in (threaded or pressed into) one of the components of the assembly.

Fixed-Limit Gage - A device of defined geometric form and size used to assess the conformance of a feature of size of a workpiece to a dimensional specification.

Flag Notes - Notes that are located with the general notes but apply only at specific areas or points on the drawing.

Flash - A geometric tolerance that limits the amount of flatness error a surface is allowed.
flatness Flatness - The condition of a surface having all of its elements in one plane.

Flatness Tolerance - A geometric tolerance that defines the allowable flatness deviation permitted on a planar surface or derived median plane.

Flats - A straight segment that interrupts an arc.

Floating Fastener Assembly - An assembly of two or more parts where two (or more) components are held together with fasteners (such as bolts and nuts), and both components have clearance holes for the fasteners.

Floating Fastener Formula - A formula used to calculate positional tolerance values in a floating fastener assembly.

T = H - F
Where:
T = position tolerance diameter (for each part)
H = MMC of the clearance hole
F= MMC of the fastener

Form Tolerance - A geometric tolerance that defines the allowable flatness deviation permitted on a planar surface or derived median plane.

Free State - The condition of a part free of applied forces.

Free State Variation - The distortion of a part after removal of forces applied during manufacture.

FRTZF - Feature related tolerance zone framework.The lower segments of a composite control.

Full Indicator Movement - The total movement of an indicator where appropriately applied to a surface to measure its variations.

Functional Dimensioning - A dimensioning approach that defines a part based on the product (fit and function) requirements.

Functional Gage - A fixed-limit gage used to verify virtual condition acceptance boundaries.

Fundamental Dimensioning Rules - A set of general rules defined by ASME for dimensioning and interpreting drawings.

Gage - A device used to measure a part characteristic.

Gage Element - A physical portion of a gage.

Gagemakers' Tolerance - The manufacturing tolerance allowed a gagemaker that is applied to gages and comparator setting masters.

Gate - A channel in a mold through which molten material flows into the mold cavity.

General Fixed Fastener Formula - (for equally distributed tolerances) is

H = F + 2T or T = 
Where: 
T = position tolerance diameter
H = MMC of the clearance hole
F = MMC of the fastener

General Notes - Notes that apply to the entire drawing; they are always numbered as a single-numbered list in the notes area of the drawing.

Geometric Characteristic Symbols - A set of 14 symbols used in the language of GD&T to describe the geometry attributes of a part.

Geometric Dimensioning and Tolerancing (GD&T) - A symbolic language used on engineering drawings and CAD models to define part geometry and communicate allowable variation.

Geometric Tolerance - The general term applied to the category of tolerances used to control form, profile, orientation, location, and runout.

Geometry Attribute - A characteristic of a feature or feature of size.

Go Gage - A fixed-limit gage that checks a feature of size for acceptance within MMC perfect form boundary.

Great Myth of GD&T - The misconception that geometric tolerancing raises product costs.

Height Gage - A measuring device used for measuring a vertical distance of a feature from a reference surface.

Implied 90° Angle - Where center lines and lines depicting features are shown on a 2D orthographic drawing at right angles, and no angle is specified.

Implied 90° Basic Angle - A 90° basic angle that applies where center lines of features in a pattern (or surfaces shown at right angles on a drawing) are located and defined by basic dimensions, and no angle is specified.

Implied Basic Zero Dimension - Where a center line or center plane of a feature of size is shown in line with a datum axis or center plane. The distance between the center lines or center planes is an implied basic zero.

Implied Datum - An assumed plane, axis, or point from which a dimensional measurement is made.

Implied Parallelism - Where two surfaces are shown parallel on a drawing and the size dimension controls the parallelism between the surfaces.

Implied Self-Datum - When a geometric tolerance implies that a feature is to be inspected relative to its perfect counterpart. Example: a position tolerance specified without a datum reference creates a relationship between the two coaxial features.

Independency Concept - Size and form are independent; Rule #1 does not apply.

Indicator Zero Block - A gage detail that has two parallel surfaces set at a set distance apart.

Individual - Notation used along with an indication of the number of places a datum feature and either a single feature of size or a pattern of features of size apply on an individual basis.

Inner Boundary (of an internal feature of size) - A worst-case boundary generated by the smallest feature of size (MMC) minus the effects of the applicable geometric tolerance and any additional tolerance (bonus) that may apply.

Inner Boundary (of an external feature of size) - A worst-case boundary generated by the smallest feature of size (LMC) minus the effects of the applicable geometric tolerance and additional tolerances (bonus) that may apply.

Irregular Feature of Size - A general term for two types of irregular features of size. Type A: a directly toleranced feature or collection of features that may contain or be contained by an actual mating envelope that is a sphere, cylinder, or pair of parallel planes.Type B: a directly toleranced feature or collection of features that may contain or be contained by an actual mating envelope other than a sphere, cylinder, or pair of parallel planes.

Item - A nonspecific term used to denote any unit or product, including materials, parts, assemblies, equipment, accessories, and computer software.

Item Identification - The part, identifying number, or descriptive identifier for a specific item along with the original design activity identification.

Least Material Boundary (LMB) - The limit defined by a tolerance or combination of tolerances that exists on or inside the material of a feature(s).
least material condition Least Material Condition (LMC) - The condition in which a feature of size contains the least amount of material everywhere within the stated limits of size.

Limit Dimensioning - Where a dimension has its high and low limits stated. In a limit tolerance, the high value is placed on top, and the low value is placed on the bottom.

Limits of Size - The specified maximum and minimum sizes.

Local Notes - Notes that are located at the specific area or point of application on the drawing.

Location - a) Center to center distance between features of size. b) Location of features of size from a datum. c) Coaxiality of features of size. d) Concentricity or symmetry of features of size from a datum axis or plane.

Max Dimension - The drafting symbol for a maximum dimension is the letters “MAX” following the dimension value; where a maximum dimension is indicated, the opposite end of the specification is usually zero.

Maximum Material Boundary (MMB) - The boundary established by the collective effects of the MMC of a datum feature and any applicable tolerances.
maximum material condition Maximum Material Condition (MMC) - The condition in which a feature of size contains the maximum amount of material everywhere within the stated limits of size.

May - Used when it is necessary to express nonmandatory provisions.

Measurement Uncertainty - The difference between the corrected measured size and the actual size. In cases where there is adequate information based on a statistical distribution, the estimate may be associated with a specific probability.

Median Point - The mid-point of a two-point measurement. 

Mismatch - The offset of features on a part caused by misalignment of opposing segments of a mold or die.

Model - A combination of design model, annotation, and attributes that describes a product.

Modifiers - Symbols or keywords that communicate additional information about the tolerancing of a part.

Monodetail Drawing - Delineates a single part. 

Movable Datum Target - A datum target with a movable datum target datum feature simulator.

Movable Datum Target Symbol - Indicates that the datum feature simulator is movable.

Multidetail Drawing - Delineates two or more uniquely identified parts in separate views or in separate sets of views on the same drawing. 

Multiple Single-Segment - When two (or more) single-segment feature control frames are stacked together. Each segment is an independent requirement.
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Multiple Single-Segment Position Tolerance - Two or more single-segment position tolerances applied to the same feature of size or pattern of features of size.

Multiple Single-Segment Profile Tolerance - Where two or more profile tolerances are applied to a surface (or collection of surfaces) relative to different datum reference frames.

NOGO Gage - A fixed-limit gage that checks a feature of size for violation of its LMC actual local size.

Nominal Size - The designation used for purposes of general identification.

Non-Feature of Size - Not considered a feature of size because the parallel surfaces are not opposed; they are offset.

Non-Opposed - Two planar surfaces are non-opposed if none of the rays projected from each surface intersect the other surface.

Non-Uniform Tolerance Zone - A maximum material boundary and least material boundary, of a unique shape, that encompasses the true profile. The method to indicate a non-uniform tolerance zone is use the term “NON-UNIFORM” to replace the tolerance value in the feature control frame.

Number of Places Symbol - Symbolic means of indicating how many places a dimension or shape apply on a drawing.

Opposed - All rays normal from each planar surface intersects the other surface.

Optical Comparator - (Often called a comparator or profile projector) is a device that applies the use of optics to measure part geometry.

Orientation - The orientation of a feature or a feature of size is its angular relationship to a datum. Orientation tolerances control parallel, perpendicular, and all other angular relationships.

Orientation Tolerance - A geometric tolerance that limits the amount of orientation error a surface, axis, or center plane is allowed.

Outer Boundary (of an external feature of size) - A worst-case boundary generated by the largest feature of size (MMC) plus the effects of the applicable geometric tolerance.

Outer Boundary (of an internal feature of size) - A worst-case boundary generated by the largest feature of size (LMC) plus the effects of the applicable geometric tolerance.

Parallel - The condition of being an equal distance apart at every point.

Parallelism - The condition where a surface, axis, or center plane is equidistant at all points from a datum plane or axis.
parallel Parallelism Tolerance - A geometric tolerance that limits the amount a surface, axis, or center plane is permitted to deviate from parallelism, relative to a datum reference frame.

Part - One item, or two or more items joined together, not normally subject to disassembly without destruction or impairment of designed use.

Part or Identification Number - The identifier assigned by the original design activity, or by the controlling nationally recognized standard, that uniquely identifies a specific item relative to that design activity.

Partial Datum Reference Frame - Where only one or two datum planes of the datum reference frame are used.

Partially Opposed - Two planar surfaces are partially opposed if some of the rays projected normal from each planar surface intersect the other surface.

Parting Line - a) The separation between the mold or die segments, flash fins, or material seepage is usually produced on the part periphery where the parting line emerges. b) A line on the drawing representing the mated surfaces of the die or mold segments.

Pattern - Two or more features or features of size to which a locational geometric tolerance is applied and is grouped by one of the following methods: nX, INDICATED, n COAXIAL HOLES, ALL OVER, ALL AROUND, between symbol, n Surfaces, simultaneous requirement.

Perpendicular - A surface, center plane, or axis at a right angle to a datum plane or axis.
perpendicularity Perpendicularity - The condition where a surface, axis, or center plane is exactly 90° to a datum plane or axis. 

Perpendicularity Tolerance - A geometric tolerance that limits the amount a surface axis, or center plane is permitted to deviate from being perpendicular to a datum. A perpendicularity tolerance can only constrain rotational degrees of freedom relative to the datum referenced.

Phantom Line - A line consisting of a pattern of a long dash, two short dashes, and a long dash. 

Physical Datum Feature Symbol - The physical boundary used to establish a simulated datum from a specified datum feature.

Planar Feature of Size - A feature of size that contains two features: the two parallel plane surfaces (such as a width or a thickness). A planar feature of size is one type of a regular feature of size; capable of producing a center plane.

PLTZF - Pattern locating tolerance zone framework.<br><br>The uppermost segment of a composite position control. The basic relationship between the features in a pattern and the referenced datums.

Plus and Minus Tolerance - Where the nominal of the dimension is given first, followed by a plus-minus expression of a tolerance.

Polygon - A closed plane figure with straight sides.

Position Tolerance - A geometric tolerance that limits the amount the center point, axis, or center plane of a feature of size is permitted to deviate from true position.

Precision Square - A gage block that has a precise 90˚ angle between the bottom surface and one of the sides of the block.

Primary Datum - The first datum referenced in a feture control frame. It is the first datum that the part contacts in a dimensional measurement.

Profile - An outline of a surface, a shape made up of one or more features, or a two-dimensional element of one or more features. 
profile of a line Profile of a Line Tolerance - A geometric tolerance that establishes a two-dimensional tolerance zone that is normal to the true profile at each line element.
profile of a surface Profile of a Surface Tolerance - A geometric tolerance that establishes a three-dimensional tolerance zone that extends along the length and width (or circumference) of the considered feature or features.
projected Projected Tolerance Zone - A tolerance zone that is projected (moved) outside of the feature of size.
radius Radius - A straight line extending from the center to the periphery of a circle or sphere.

Reference Dimension - a) A repeat of a dimension b) A dimension derived from other values shown on the drawing or on related drawings. One method for identifying a reference dimension on drawings is to enclose the dimension within parentheses.

Regardless of Feature Size - The term that indicates a geometric tolerance or datum reference applies at any increment of size of the actual mating envelope of the feature of size. 

Regardless of Material Boundary - Indicates that a datum feature simulator progresses from the MMB to the LMB until it makes contact with the extremities of a feature(s). 

Regular Feature of Size - One cylindrical or spherical surface, a circular element, a set of two opposed (or partially opposed) parallel elements, or opposed (or partially opposed) parallel surfaces, each of which is associated with a directly toleranced dimension (size dimension). 

Related Actual Mating Envelope - A similar perfect feature counterpart expanded within an internal feature of size, or contracted about an external feature of size, while constrained in either orientation or location (or both) to any applicable datums. 

Related Actual Minimum Material Envelope - A similar perfect feature counterpart contracted about an internal feature(s) or expanded within an external feature(s) while constrained within orientation or location (or both) to the applicable datum(s). 

Restraint - The application of force(s) to a part to simulate its assembly or functional condition resulting in possible distortion of a part from its free-state condition. 

Right-Hand Rule - The right-hand rule works as follows: if you hold the back of your right hand against a drawing and hold the thumb and index finger at 90° to each other:

  • The thumb pointing to the right represents the X-axis positive direction.
  • The index finger pointing to the top of the drawing represents the Y-axis positive direction.
  • The middle finger pointing at you represents the Z-axis positive direction.

Rotation - Angular movement about an axis.

Roundness (Circularity) Gage - A precision spindle machine used to measure the out of roundness (circularity deviations) of a surface of revolution.

Rule #1 - The form of an individual regular feature of size is controlled by its limits of size.

Rule #2 - RFS applies with respect to the individual tolerance, and RMB applies, with respect to the individual datum feature reference, where no modifying symbol is specified.

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Runout - The high to low point deviation of the surface elements relative to a datum axis.

Scale - The ratio of the object size as drawn to its full size.

Secondary Datum - The second datum referenced in a feature control frame. It is the second datum that the part contacts in a dimensional measurement.

Separate Requirement - This tolerance is verified as a separate inspection item. The part must meet this requirement to be accepted.

Shall - Establishes a mandatory requirement.

Should - Used when it is necessary to express nonmandatory provisions.

Simulated Datum - A datum established from a physical datum feature simulator.

Simultaneous Requirement - Where two or more geometric tolerances have identical datum references and are considered a pattern.

Sine Bar - A precision inspection tool used to orient parts at any angle, usually between zero and sixty degrees. It is so named because the sine of the angle determines the height of a stack of gage blocks used to set the angle.

Six Degrees of Freedom - Rotation around the X, Y, or Z axis, and movement along the X, Y, or Z axis.

Size Dimension - A dimension across two opposed (or partially opposed) surfaces, line elements, or points.

Special-Case Feature of Size Datum - When a feature of size datum feature is referenced at MMC, but simulated in the gage at a boundary other than MMC. 

Spherical Diameter - The length of a straight line that passes through the center of a sphere and touches two points on its edge. 

Spherical Radius - A radius that generates a segment of a sphere. 

Spine - A simple (non self-intersecting) curve. 

Spotface - The min size of the flat on a flat-bottomed diameter. 
straightness Straightness - The condition where an element of a surface or a derived median line is a straight line. 

Straightness of a Line Element - The condition where each line element (or axis or centerplane) is a straight line.

Straightness Tolerance - A geometric tolerance that, when directed to a surface, limits the amount of straightness error allowed in each surface line element. A straightness tolerance is applied in the view where the elements to be controlled are represented by a straight line.

Surface Interpretation - The tolerance zone is a virtual condition (acceptance boundary), located at true position, which the surface(s) of the tolerance features(s) of size must not violate.

Surface Plate - A solid, flat plate used as the main horizontal reference plane (datum feature simulator, see Chapter 13) for precision inspection and tooling setup.

Symmetrical Relationship - Where the location deviation of the center plane of a feature of size is being defined relative to a datum center plane. In these cases, a position tolerance may be used to limit the offset between the center planes.
symmetry Symmetry - The condition where all the median points of all opposed correspondingly located elements of two or more feature surfaces are congruent with a datum axis or center plane.

Symmetry Tolerance - A geometric tolerance that defines the permissible deviation that median points of all opposed correspondingly located elements of two or more feature surfaces are permitted to vary from a datum axis or center plane.

Tangent Plane - A plane that is tangent to the high points of the surface.

Tangent Plane Modifier - The geometric tolerance only applies to the tangent plane of the toleranced surface.

Tertiary Datum - The third datum referenced in a feature control frame. It is the third datum that the part contacts in a dimensional measurement.

Theoretical Datum Feature - The theoretically perfect boundary used to establish a datum from a specified datum feature.

Third Angle Projection - The formation of an image or view upon a plane of projection placed between the object and the observer.

3-2-1 Rule - A part will have a minimum of three points of contact with its primary datum plane, two points minimum contact with its secondary datum plane, and a minimum of one point of contact with its tertiary datum plane.

Tolerance - The total amount a specific dimension is permitted to vary. The tolerance is the difference between the maximum and minimum limits.

Tolerance Accumulation - A condition where the tolerances from several dimensions combine to result in a greater amount of tolerance for a part distance.

Tolerance Analysis Chart - A chart that graphically displays the available tolerances of a feature of size as defined by the drawing specifications.

Tolerance of Position Control - A geometric tolerance that defines the location tolerance of a feature of size from its true position.

Tolerance Stack - A calculation that determines the theoretical maximum or minimum distance between two features on a part or in an assembly.

Tolerance Zone - The area (zone) that represents the total amount that part features are permitted to vary from their specified dimension.
total runout Total Runout - The area (zone) that represents the total amount that part features are permitted to vary from their specified dimension.

Total Runout Tolerance - A geometric tolerance that limits the high to low point deviation of all surface elements of a cylindrical surface, or all surface elements of a planar surface that is perpendicular to and intersects the datum axis.

Translation - The ability to move without rotating.

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

True Position - The theoretically exact location of a feature of size defined by basic dimensions.

True Profile - A profile defined by basic radii, basic angular dimensions, basic coordinate dimensions, basic size dimensions, undimensioned drawings, formulas, or mathematical data, including design models. 

Unequal Bilateral Tolerance - A tolerance in which the allowable variation from the nominal value is not the same in both directions.

Unequal Disposed Profile Symbol - Indicates a unilateral or unequally disposed profile tolerance.

Unilateral Tolerance - Where the allowable variation from the nominal value is all in one direction and zero in the other direction.

Unilateral Tolerance Zone - A tolerance zone that is offset to one side of the material, either “all outside” or “all inside” of the material.

Unrelated Actual Mating Envelope - A similar perfect feature counterpart expanded within an internal feature of size or contracted about an external feature of size and not constrained to any datums.

Unrelated Actual Mating Envelope - External - A similar perfect feature(s) counterpart of smallest size contracted about an external feature(s) and not constrained to any datum(s).

Unrelated Actual Mating Envelope - Internal - A similar perfect feature(s) counterpart of largest size that can be expanded within an internal feature(s) and not constrained to any datum(s).

Unrelated Actual Minimum Material Envelope - A similar perfect feature counterpart contracted about an internal feature(s) or expanded within an external feature(s) and not constrained to any datum reference frame.

Variable Gaging - Any gaging operation that measures part variation and provides a quantitative value of the variation.

Virtual Condition (VC) - A fixed-size boundary generated by the collective effects of a considered feature of size’s specified MMC or LMC and the geometric tolerance for that material condition.

Will - Establishes a declaration of purpose on the part of the design activity.

Worst-case Boundary (WCB) - A general term used to refer to an inner boundary, outer boundary, or virtual condition.

Zero Tolerance at MMC - A dimensioning method that takes the tolerance stated in the feature control frame, combines it with the size tolerance, and states a zero tolerance in the feature control frame.


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