ORIEN

TATIO

NFO

RMLO

CATIO

NPR

OFILE

RUNO

UT

Prima

ry

Second

ary TertiaryA

DatumThe controlling feature (axis, surface, plane or point) where GD&T is referenced to. This feature is held xed when the part is measured.

RULE # 1 OF GD&T: ENVELOPE PRINCIPLE Where only normal dimensional tolerance of size exists on a part, the variation of size and the geometric form must not extend past dimensional tolerance zone.

Rule # 1 ExplainedRule # 1 means the part in its virtual condition (size + geometry) cannot extend beyond the dimensional tolerance on the drawing. The part envelope is the full limit of all geometry.

Example: If circularity was called on the example to the left, but the part is at its maximum diameter, the circularity must be near perfect as to not extend the boundary of the size (diameter) tolerance beyond the upper boundary.

Cannot exceed boundaries, no matter what the geometric tolerances are.

1. Leader Arrow2. Geometric Control

Symbol3. Diameter Symbol4. Geometric Tolerance

5. Modier/Feature of size

6. Primary Datum7. Secondary Datum8. Tertiary Datum

6 degrees of freedomAll the possible translation and rotation movements a part can make in free state. X,Y,Z movement and rotation about the X,Y and Z Axes.

Datum Reference FrameThe concept of controlling the degrees of freedom though datum features using perpendicular blocks in a xture that represent the datum controls.

To control all 6 degrees of freedom:Primary Datum: 3 Points of contactSecondary Datum: 2 Points of contactTertiary Datum: 1 Point of contact

Tolerance Zone The total tolerance listed in the feature control frame where all the points of the referenced feature must lie. Tolerance zones are the total range of the tolerance. (sum of both directions)

0.030 M1

2 3 4 5 6 7 8

10.00.1

10.1

9.9

Rule # 1 exceptionsThis does not apply to features of size under , or if the independence symbol is used.

M L

Virtual ConditionThe total sum of all size and geometric tolerances on a part that form the "worst" case limit of all the tolerances. For internal features like a hole:Virtual Condition = - Geometric tolerance

For external features like a pin:Virtual Condition = + Geometric tolerance

M

M

RULE # 2: IMPLIED REGARDLESS OF FEATURE SIZERegardless of Feature Size is always implied on geometric tolerances unless otherwise specied by Least Material Condition or Maximum Material Condition .

ML

A B C

A

A

0.030

0.030

0.030

0.030

0.030

0.030

100.050

M

A

A

0.030

0.030

0.030

0.030

30.0

0.030

20.0

30.0

20.0

Two parallel planes0.030 apart

Two concentric circles0.030 apart

Two parallel lines0.030 apart

Two parallel planes0.030 apart

Two parallel planes0.030 apart

Datum A

AxisTolerance Zone

at

100.050

100.050

0.030

M

Cylindrical Tolerance Zone0.030 when Part = 10.0500.130 when Part = 9.950

Datum A

Datum A60

Datum A

Datum A

Two concentric cylinders0.030 apart

Two parallel planes0.030 apart

Two parallel lines0.030 apart

Datum B

Datum A

Datum A

Datum A plane

Tolerance Zone

Two parallel planes0.030 apart

Datum B

Part

Gauge

Flat datum block(Datum A)

Flat datum block(Datum A)

ActualPin Position

True position

Tolerance Zoneof Hole Gauge

Datum axisMeasured axis

Hole Gauge = Max feature + tolerance

A

A

A

A0.030

0.030

0.030

A

Two parallel planes0.030 apart

A

Datum AFixed axially+ Rotated

A

Datum AFixed axially+ Rotated

Datum AFixed + Rotated

Normal/Circular runoutonly checks individual sections independent of each other

A

A

Gauge must follow true prole.

Prole is usually measured with a CMM.

Gauge ID = 10.080

Cylinder Gauge ID = M +

Bonus tolerance

60

GaugeBlock

60

Gauge must follow true prole.

Prole is usually measured with a CMM.

90

Gauge pininsertedperpendicular to datum

Pin Gauge = 9.920(9.950 - 0.030)

Pin Gauge OD = M

0.030

Part (actual) position

Truecenter

Measure X and Y location and compare to the true position.

This formula must be less thanthe True Position tolerance

(Actual X - True X)2 + (Actual Y + True Y)2Y

X

Actual Y

True Y

Actual XTrue X

The following is usually done with a CMM:1. Determine Datum axis2. Measure referenced surface3. Determine if

central axis fall in TZ

The following is usually done with a CMM:1. Determine Datum plane2. Measure both

surfaces of features3. Determine if

midpoints fall in TZ

ActualHole Position

True position

Tolerance Zoneof Pin Gauge

Gauge

Part

Pin Gauge = Min hole tolerance

Datum AFixed + Rotated

All points are to bein spec at all times

Actual True

60

A

A

A

A

A

A

A

A

B

B

A

A

B

B

A

A

B

B

A

A

A

A

A

A

A

B

B

C

C

M

0.030 M

0.030

Straightness(Surface)

Flatness

Circularity

Cylindricity

Parallelism

Straightness(Axis under )M

Perpendicularity(Axis under )M

Perpendicularity(Feature)

Angularity

Profile of a line

True Position

Concentricity

Symmetry

Runout

Total Runout

Profile of a surface

True Position (Maximum Material Condition)

M

M

M

SYMBOL NAME ON DRAWING MEANING GAUGING

Copyright 2014 GD&T Basics - Chart designed by Andrea Barbieri

Provided by GD&T Basics - For the best GD&T training online, visit www.gdandtbasics.com

GD&T Symbols and Guidelines Cheat Sheet

DESCRIPTION DATUM REQUIREDMMC OR LMC APPLICABLE? POINTS TO REMEMBER

2D Tolerance Zone: Two parallel lines

No No (Surface) Tolerance must be less than dimensional tolerance. RFS applies in surface condition.

3D Tolerance Zone: Cylindrical Boundary within which the central axis must entirely lie.

No MMC (Axis) Envelope Principle (Rule #2) no longer applies. Functional Gauge is allowed if MMC is called to control both size and geometry.

3D tolerance Zone: Two parallel planes, where the entire surface must lie.

No No Rule#1 still applies. If a at surface is at its maximum size dimension, the atness must be perfect. Tolerance must be less than dimensional tolerance. Different from Parallelism: No Datum or references.

2D Tolerance Zone: Coaxial circles which all elements must fall into.

No No Can be measured in multiple locations to determine if each cross section is round. Cannot control taper. Tolerance must be less than dimensional tolerance.

3D Tolerance Zone: Coaxial cylinders which all elements on the entire cylinder must fall into.

No No Combination of straightness and circularity. Can control taper and straightness of part. Tolerance must be less than dimensional tolerance.

2D or 3D Tolerance Zone: Parallel lines or planes, equally set apart, that are controlled parallel to a datum feature.

Yes No (Surface)Yes (Axis)

Controls orientation as well as straightness (2D) or Flatness (3D). MMC can also be applied to parallelism when controlling an axis.

2D or 3D Tolerance Zone: Parallel lines or planes, equally set apart, that are set perpendicular (90) to a datum feature.

Yes No (Surface) Controls orientation as well as straightness (2D) or Flatness (3D). MMC can also be applied to parallelism when controlling an axis. (see below).

3D Tolerance Zone: Cylindrical boundary that is directly perpendicular to the datum plane. The derived axis of the referenced feature must entirely fall in this zone.

Yes Yes (Axis) Envelope Principle (Rule #1) no longer applies but hole must fall within size limits. Functional Gauge is allowed if MMC is called to control both size and geometry.

2D or 3D Tolerance Zone: Parallel lines or planes, equally set apart that are set at a speci ed angle.

Yes No (Surface)Yes (Axis)

Parallelism and perpendicularity are speci c forms of angularity. Tolerance Zone is in distance units, NOT an angle.

2D Tolerance Zone: Two uniform parallel lines (usually curved) that follow the true pro le of the feature. All points along the pro le line must lie between this tolerance zone.

Optional No Tolerance can be Unilateral with the callout to allow the tolerance zone to be unsymmetrical. Commonly used on curved surfaces or complex geometry.

3D Tolerance Zone: Two uniform parallel surfaces (usually curved) that follow the true pro le of the feature. All points along the pro le surface must lie between this tolerance zone.

Optional No Tolerance can be Unilateral with the callout to allow the tolerance zone to be unsymmetrical. Commonly used on curved surfaces or complex geometry. Also may be used to control how two surfaces are with respect to each other.

2D or 3D Tolerance Zone: Cylindrical or circular boundary where the center of a round feature must lie, with respect to the theoretically true location.

Yes Yes Tolerance must be less than dimensional tolerance. RFS applies in surface condition.

3D Tolerance Zone: Cylindrical boundary, or parallel planes, where the entire axis or median plane of a feature must lie, with reference to its theoretical true location. (In this example it is for an axis)

Yes Yes Envelope Principle (Rule #1) no longer applies. Can control perpendicularity and straightness as well as size. Very common for use with functional gauging in MMC.

3D Tolerance Zone: Cylindrical boundary where all the reference features median axis points must lie. Boundary is controlled with reference to the central axis of the datum feature.

Yes No Very dif cult to measure for! Use only when inertial effects need to be controlled or part cannot be measured with runout. Median points of reference feature are held in control by datum axis.

3D Tolerance Zone: Two parallel planes where all the median points of the referenced features must lie. Boundary is controlled with reference to the central plane of the datum feature.

Yes No Very dif cult to measure for! Use true position with orientation or form control to specify. Median points of reference feature are held in control by datum median plane.

2D Tolerance Zone: Two concentric circles that are controlled with relation to the datum axis, where all points on the reference feature must lie when the part is rotated.

Yes No RFS always applies. Combination of Concentricity and Circularity. Very useful to prevent wobble of cylindrical parts.

3D Tolerance Zone: Two concentric cylinders that are controlled with relation to the datum axis, where all points on the reference feature must lie (all at once) when the part is rotated.

Yes No RFS always applies. Combination of Concentricity and Cylindricity. Controls two features together during rotation. Very useful to prevent wobble of cylindrical parts but is a very tight control. Controls two features together during rotation.

Features of Size Condition

RFS - Regardless of Feature SizeGeometric tolerances are as-is and need to be within tolerance regardless of the size of the feature. No additional allowances for features of size. No functional gauging is allowed.This is the default condition on all GD&T unless otherwise speci ed - See Rule # 2 below.

M Maximum Material Condition (MMC)The speci c dimension within the tolerance range of a feature where the maximum amount (volume) of material would be in the part.

For an internal feature like a hole - Smallest SizeFor an external feature like a pin - Largest Size

L Least Material Condition (LMC) The speci c dimension within the tolerance range of a feature where the least amount (volume) of material would be in the part.

For an internal feature like a hole - Largest SizeFor an external feature like a pin - Smallest Size

Bonus ToleranceWhen a feature is controlled under M the entire virtual condition is established. (See virtual condition below). If there is a difference between the actual value and MMC, this bonus tolerance may then be added to the geometrical tolerance.

For an internal feature like a hole:Bonus tolerance = Actual feature size MMC.For internal features, the smallest diameter is the MMC, and you gain bonus tolerance as you get larger.

For an external feature like a pin:Bonus tolerance = MMC Actual feature size.For external features, the largest diameter is the MMC, and you gain bonus tolerance as you get smaller.

Other Datum Symbols

A14 Datum TargetReference to locate datum points needed

to create a theoretical datum plane in order to measure the part.

Target PointsSpeci c measurement location for the datum targets shown on the current drawing view.

Additional Symbols used in GD&T

P Projected ToleranceThe tolerance zone is extended out beyond the limit of the part, to a speci ed location. Used commonly with perpendicularity to represent the virtual condition of a pin or stud.

F Free StateThe part may not be restricted during inspection.

IndependencyRule #1 is overridden and the parts geometric tolerance is no longer restricted by the limits of size.

ST Statistical ToleranceThe tolerances of the part are derived from statistical analysis of individual components and will vary depending on a calculation done for assembly. Usually the Pp or Ppk is speci ed for the given assembly.

T Tangent PlaneA tangent plane is established on the surface of a part based on the parts orientation. When called, only the virtual tangent plane needs to be within the tolerance zone, and not all the surface points need to be within.

10.5 Basic DimensionsDimensions that are listed without a tolerance and in a rectangular box that represent the true location of a feature to locate a tolerance zone. Used commonly with true position.

Diameter Symbol

Pro le Speci c Callouts

All Around SymbolIndicates that the geometric tolerances apply to every surface around the part in the speci ed view.

U Unilateral SymbolWhen called the tolerance zone for a pro le is not symmetrical with respect to the true pro le. The value following the symbol is the amount of shift the pro le is allowed in the direction of max material condition.

Between SymbolSpeci es the exact limits of the surface or line that the pro le tolerance controls. This helps clear up where exactly the pro le needs to be within tolerance.