GD&T Symbols, Definitions Chart ASME Y14.5-2009 Training
The following are definitions commonly used throughout industry when discussing GD&T or composing engineering drawing notes. Many of the definitions are not official ASME, ANSI or ISO terminology.
Accept where noted, definitions are applicable to ASME &14.5M-1994 and ASME ASME Y14.5-2009.
** ISO 1101 exclusively associated definitions are noted as such.
|Actual Size - Actual size is the measured size of the produced feature.|
|Angularity - Angularity is the condition of a surface, axis, or center plane, which is at a specified angle (other than 0, 90, 180 or 270 deg.) from a datum plane or axis. Symbol:|
|All Around - Indicates that a tolerance applies to surfaces profile all around the part outline.|
|All Over - Indicated that indicated geometric or other specification applies all surface elements or features.|
Basic Dimension - A basic dimension is a theoretically exact value used to describe the exact size, profile, orientation or location of a feature. A basic dimension should always associated with a feature control frame or datum target. Block tolerance does not apply and the applicable tolerance will be given within the feature control frame. Basic dimensions are enclosed within a box. Symbol:
|Between - to indicate that a profile tolerance applies to several contiguous features, letters may designate where the profile tolerance begins and ends. These letters are referenced using the between symbol (since 1994) or the word between on drawings made to earlier versions of the Standard.|
|Bilateral Tolerance - A bilateral tolerance is a tolerance in which variation is permitted in both directions from a specified nominal size or dimension (example ± .005).|
|Center Plane - Center plane is the middle or median plane of a feature of size.|
Circularity - Circularity, also called "Roundness" describes the condition on a surface of revolution (cylinder, cone, or sphere) where all points of the surface intersected by any plane are; (1) perpendicular to a common axis (cylinder, cone), (2) passing through a common center (sphere) are equidistant from the center. Symbol:
|Circular Runout - Circular runout is the composite deviation from the desired form of a part surface of revolution through one full rotation (360 deg) of the part on a datum axis. Circular runout is most often specified on an engineering drawing where the referenced rotates relative to the specified datum feature.|
|Clearance Fit - A clearance fit is one having limits of size defined such that a clearance exists between mating parts when assembled.|
Concentricity - Concentricity describes a condition in which two or more features (cylinders, cones, spheres, etc.) in any combination have a common axis. Measurement requirements for concentricity involves the complex task of mapping the referenced feature by way of opposed point measurements. A through understanding of the measurement process should be investigated before defining feature relationships using concentricity.
|Coaxial - Coaxial describes a condition where two or more features have the same axis or centerline.|
|Coaxiality - ISO 1101|
|Coordinate Dimension - (1) Either of two coordinates that locate a point on a plane and measured its distance from either of two intersecting straight-line axes along a line parallel to the other axis. (2) Any of three coordinates that locate a point in space and measure its distance from any of three intersecting coordinate planes measured to that one of three straight-line axes that is the intersection of the other two planes. Often the application of dimension origin is referred to as a coordinate dimension.|
|Continuous Feature - Indicates that associated features are to be dimensionally controlled as a single continuous feature.|
|Controlled Radius - The as-manufactured controlled radius surface must be a fair curve without having sharp
corners and reversals.
|Coplanar - Coplanar describes a condition of two or more surfaces having all elements in the same plane.|
|Cylindricity - Cylindricity describes a condition of a surface of revolution in which all points of a surface are equidistant from a common axis. Symbol: . Cylindricity controls a cylindrical features element such that the total variations are minimized during manufacturing.|
|Datum - Datum's are points, lines, planes, cylinders, axes, etc., from which the location or geometric relationship of other features may be established or related.|
|Datum Axis - the datum axis is the theoretically exact centerline of the datum cylinder as established by the extremities or contacting points of the actual datum feature cylindrical surface or the axis formed at the intersection of two datum planes.|
|Datum Feature - A datum feature is the actual surface component used to establish a datum. The datum feature is specified on an engineering drawing using accepted methods and is used and establish specific origin-feature relationships.|
|Datum Line - A datum line is that which has length but no breadth or depth, such as, an intersection line of two planes, centerline or axis of holes or cylinders and/or reference line for functional tooling or gauging purposes.|
|Datum Point - A datum point is that which has position, but no extent; such as, the apex of a pyramid or cone, center point of a sphere or reference point on a surface for functional tooling or gauging purposes.|
|Datum Reference - A datum reference is a datum feature. ISO 1101|
|Datum Reference Plane - is a set of three mutually perpendicular datum planes or axis established from the simulated datum in contact with datum surfaces or features and used as a basis for dimensions for designs, manufacture, and inspection measurement.|
|Datum Simulator - A datum simulator is a surface of adequate precision oriented to the high points of a designated datum from which the simulated datum is established. Examples: gage pin, block, surface of granite block.|
|Diameter Symbol - the diameter symbol indicates a circular feature when used on the field of a drawing or indicates that a defined tolerance is diametrical when used in a feature control frame.|
|Dimension - A dimension is a numerical value expressed in appropriate units of measure and indicated on a drawing.|
Extracted Integral Feature - An approximated representation of the real feature (integral), obtained by extracting a finite number of points from the real feature (integral). This extraction is performed in accordance with specified conventions. Definition Per. ISO 1101-2004 (E)
|Feature - Features are specific component portions of a part and may include one or more surfaces, such, as holes, screw threads, profiles, faces or slots. Features may be individual or interrelated.|
|Feature of Size - One cylindrical or spherical surface, or a set of two plane parallel surfaces, each of which is associated with a size dimension.|
|Feature Control Frame - The feature control frame is a rectangular box containing the geometric characteristics symbol, specified tolerance and datum's references as required.|
|Fit - Fit is a general term used to signify the range of tightness or looseness which may result from the application of a specific combination of allowances and tolerance in the design of mating part features. Fits are of four general types: interference, transition, line and clearance.|
Flatness - Flatness is the condition of a surface having all elements in one plane.
|Form Tolerance - A form tolerance states how far an actual surface is permitted to vary from desired geometric form. Expressions of these tolerances refer to limits of size, flatness, straightness, parallelism, perpendicularly, angularity, roundness, cylindricity, profile of a surface and profile of a line.|
|Free State - Free state is the variation of form to describe the distortion of a part after removal of forces which restrain the part during manufacturing processes.|
|Free State Variations - Free state variation is a term used to describe the distortion of a part after removal of forces applied during manufacture or assembly.|
|Full Indicator Movement FIM - The total movement of an dial or digital indicator where appropriately applied to a surface feature while measuring surface variations. See TIR (Total Indicator Reading).|
|Geometric Characteristics - Geometric characteristics refer to the basic elements or building blocks which form the language of geometric dimensioning and tolerancing. Generally, the term refers to all the symbols used in form, runout, profile and locational tolerancing.|
Geometrical Characteristics - Geometrical characteristics refer to the basic elements or building blocks, which form the language of geometric dimensioning and tolerancing. Generally, the term refers to all the symbols used in form, runout, and locational tolerancing. Definition Per. ISO 1101
|Geometric Tolerance - The general term applied to the category of tolerances used to control form, profile, orientation, location, and runout.|
|Geometric Tolerance - The general term applied to the category of tolerances used to control form, profile, orientation, location, and runout. Definition Per. ISO 1101|
|Independency - This symbol invokes "Principle of Independency" This principle sets no limits to the number of errors of form possessed by individual features of a work piece. International designer, except the USA, use this principle.|
|Interference Fit - An interference fit is one having limits of size so prescribed that an interference will occurs when mating parts are assembled.|
Least Material Boundary (LMB) - This term implies that the condition of a datum feature of size wherein it contains the least (minimum) amount of material for the stated limits of size; examples, largest hole size and smallest shaft size. It is the opposite materials condition to maximum material condition (MMB).
Least Material Condition (LMC) - This term implies that the condition of a feature of size wherein it contains the least (minimum) amount of material for the stated limits of size; examples, largest hole size and smallest shaft size. It is the opposite materials condition to maximum material condition (MMC).
Least Material Requirement LMR - This term implies that condition of a part feature of size wherein it contains the least (minimum) amount of material, examples, largest hole size and smallest shaft size. It is opposite to maximum material requirement (MMR). Definition Per. ISO 1101
|Least Material Size LMS - Condition a feature of size where the least amount of material is present for stated limits of size. Part would weight the least amount when feature is manufactured at this size. Definition Per. ISO 1101|
|Least Material Virtual Size LMVS - Size generated by the cumulative effect of LMS and applicable geometrical tolerance. For shafts (external feature of size) LMVS = LMS - Geometrical Tolerance For hole (internal feature of size) LMVS = LMS + Geometrical Tolerance.|
|Limit Dimensions - In limit dimensioning only the maximum and minimum dimensions are specified. When used with dimension lines, the high limit is placed over the low limit. When used with a leader line or note, the low limit precedes the high limit.|
|Limits of Size - The specified maximum and minimum size of a given feature.|
|Limits of Size Concept - The limits of size concept calls for perfect form at maximum material condition. Also called Rule #1.|
|Line to Line Fit - A line fit is one having limits of size so prescribed that surface contact or clearance may result when mating parts as assembled.|
|Location Tolerance - A location tolerance states how far or near a feature may vary from the perfect location implied by the drawing as related to datum's or other features. Expressions of these tolerances refer to the category of geometric characteristics containing position, concentricity, and symmetry.|
|Maximum Material Boundary: (MMB) Maximum material condition is that condition of a part datum feature wherein it contains the maximum amount of material within the stated limits of size. That is: minimum hole size and maximum shaft size.|
|Maximum Material Condition: (MMC) Maximum material condition is that condition of a part feature wherein it contains the maximum amount of material within the stated limits of size. That is: minimum hole size and maximum shaft size.|
|Maximum Material Requirement MMR - Maximum material requirement is that condition of a part feature wherein it contains the maximum amount of material within the stated limits of size. That is: minimum hole size and maximum shaft size. Definition Per. ISO 1101|
Maximum Material Size MMS - Condition of a feature of size where the maximum amount of material is present for stated limits of size. Part would weight the most when feature is manufactured at this size. Definition Per. ISO 1101
|Maximum Material Virtual Condition MMVC - Maximum materials virtual size is generated by the cumulative effect of MMS and applicable geometrical tolerance. For shafts (external feature of size) MMVS = MMS + Geometrical Tolerance For hole (internal feature of size) MMVS = MMS ??? Geometrical Tolerance. Definition Per. ISO 1101|
|Maximum Material Virtual Size MMVS - Maximum material virtual size is generated by the cumulative effect of MMS and applicable geometrical tolerance. For shafts (external feature of size) MMVS = MMS + Geometrical Tolerance For hole (internal feature of size) MMVS = MMS ??? Geometrical Tolerance. Definition Per. ISO 1101|
|Modifier - A modifier is the term used to describe the application of MMC, LMC Free State, Projected Tolerance Zone, or Common Feature modifiers to an applied tolerance or datum feature. A modifier alters the applicability of the specified datum or feature by restricting the application to a specific condition and allowing a variable tolerance boundary under specific conditions|
|Nominal Size - The nominal size is the stated designation which is used for the purpose of general identification, examples: 1.400, .050 . The term is used in a general conversation about the materials or often to indicate the target as-manufactured size of a feature of size.|
|Parallelism - Parallelism is the condition of a surface, line, or axis which is equidistant at all points from a datum plane or axis. Parallelism tolerance may be applied to any combination of features axis t- surface, surface to axis, axis to axis et cetera.|
|Perpendicularity - Perpendicularity is the condition of a surface, axis, or line, which is 90 deg. from a datum plane or a datum axis. Often, industry individuals use the terminology "Squareness" as a substitute for perpendicularity.|
Position Tolerance - Position tolerance defines a zone within which the axis or center plane of a feature is permitted to vary from true (theoretically exact) position. Symbol:
|Principle of Independency - This principle sets no limits to the number of errors of form possessed by individual features of a work piece.|
Profile Any Line - Profile any line is the condition permitting a uniform amount of profile variation, ether unilaterally or bilaterally, along a line element of a feature. Definition Per. ISO 1101
Profile Any Surface - Profile any surface is the condition permitting a uniform amount of profile variation, ether unilaterally or bilaterally, on a surface. Definition Per. ISO 1101
Profile of a Line - Profile of a line is the condition permitting an amount of surface element variation ether unilaterally or bilaterally along a line element of a feature.
|Profile of Surface - Profile of a surface is the condition permitting an amount of surface 3D variation ether unilaterally or bilaterally of a surface.|
Projected Tolerance Zone - A projected tolerance zone applies to a feature, such as pin, stud, screw, or similar. The projected tolerance zone is a tolerance boundary that extends above or beyond the surface of the part within which the controlling element of the feature must fall within - axis of a hole for example.
|Reference Dimension - A dimension, usually without tolerance that is used for information purposes only. It does not govern production or inspection operations. A reference dimension is a repeat of a dimension or is derived from other values on the drawing or related drawings.|
|Regardless of Material Boundary - (RMB) - This is the condition where the stated tolerance limits must be met irrespective of as built datum feature size or location.|
|Regardless of Feature Size - (RFS) - This is the condition where the stated tolerance limits must be met irrespective of as built feature size or location.|
Roundness - Roundness, also called circularity describes the condition on a surface of revolution (cylinder, cone, or sphere) where all points of the surface intersected by any plane are; (1) perpendicular to a common axis (cylinder, cone), (2) passing through a common center (sphere) are equidistant from the center.
|Runout Tolerance - Runout tolerance states how far an actual surface of a feature is permitted to deviate from the desired form implied by the drawing during one full rotation of the part on a datum axis.|
|Size Tolerance - A size tolerance states how far individual features may vary from the desired size. Size tolerances are specified with ether unilateral, bilateral or limit tolerance methods.|
|Specified Datum - A specified datum is a surface or feature identified with a datum identification symbol or note.|
|Squareness - Squareness is a general term to describe or define the variations in angle between two surfaces or features oriented ninety degrees to each other. Squareness is roughly equivalent to Perpendicularity, however the perceived definition may vary depending on ones industry and experience.|
|Statistical Tolerance - Features identified as statistically toleranced shall be produced with statistical process controls.|
Straightness - Straightness describes a condition where a line element of a surface, axis, or center plane is a straight line.
|Square - Feature nominal size is square.|
|Symmetry - Symmetry is a condition in which a feature (or features) are symmetrically disposed about the center plane of a datum feature.|
|Tangent Plane - Tangent plane is a simulated flat plane that contacts the high points (tangent) of a surface for orientation of a datum or tolerance.|
|Transition Fit - A transition fit is one having limits of size so prescribed that either a clearance or an interference may result when mating parts as assembled.|
|Translation - Modifier indicating that associated datum feature can "translate" or move along a define axis.|
Tolerance Control Frame - The Tolerance Control Frame symbol is a rectangular box containing the geometric characteristics symbol, and the form, runout or location tolerance. If necessary, datum references and modifiers applicable to the feature or the datum's are also contained in the box. Definition Per. ISO 1101
|Total Runout - Total runout is the simultaneous composite control of all elements of a surface at all circular and profile measuring positions as the part is rotated through 360. Symbol:|
|Unilateral Tolerance - A unilateral tolerance is a tolerance in which variation is permitted only in one direction from the specified dimension, example, 1.400 +.000/ -.006."|
|Virtual Condition (Size) - The boundary generated by the collective effects of MMC, size limit of a feature and any associated geometric tolerance, virtual condition must be considered in determining the fit between mating parts. The term "virtual condition" is preferred over "virtual size."|