This PPT discuss the 14 geometric symbols used in GD&T classified under five controls. Only important points are mentioned. Kindly mention, if any other important points are missed out. The sources of the content (including pics) are from various sites which details GD&T. The PPT with modifiers and additional symbols (in detail) will be updated soon.

1. Symbols of GD&T (in detail)
SREELAKSHMY V.U (B.E)

2. There are 14 geometrical characteristics symbol which controls the
features in GD&T. They are classified under five controls and are
given:
1. FORM
• Straightness
• Flatness
• Circularity
• Cylindricity
2. ORIENTATION
• Angularity
• Perpendicularity
• Parallelism
3. LOCATION
• Position
• Concentricity
• Symmetry
4. PROFILE
• Profile of a line
• Profile of a surface
5. RUN OUT
• Circular Run out
• Total Run out

3. Straightness
• In this feature, all elements are proposed to be in the straight line
• Straightness error is the distance between two parallel lines
which include all elements of a line
• Straightness control is a geometric tolerance that when directed
to a surface that limit the amount of straightness error
• Straightness control requires no datum reference and modifiers
(MMC,LMC, P, T)
• It controls each line independently and separately
• If tolerance zone for straightness is applied to a FOS is a cylinder,
diameter modifier is used
• If modifier is given in the frame, then the condition is used to
describe the axis of FOS

4. Flatness
• In this feature, all elements are supposed to be in one plane
• Flatness error is the distance between two parallel planes
which include all elements of a surface (High and low points)
• Flatness control is a geometric tolerance that limits the
amount of flatness error
• Flatness feature requires no datum and no modifiers. And it
must be applied to a planar surface
• The distance between the parallel plane is determined by the
flatness control tolerance value

5. Circularity
• It is a condition where all points of a surface of
revolution at any section perpendicular to an axis are
equidistant from the axis
• Circularity error is the radial distance between two co-
axial diameters which include all elements of a circular
feature
• Circularity control limits the amount of circularity error
• Circularity feature requires no datum reference,
modifiers (M,L,P,T)
• It controls each circular element independently
• Tolerance zone for a circularity control applies to a
diameter in two co-axial circles
• Circularity control do not over ride Rule #1

6. Cylindricity
• It is the condition of a surface of revolution in which all points of the
surface are equidistant from a common axis
• Cylindricity error is the radial distance between two co-axial cylinders
which includes all elements of a cylindrical surface.
• Cylindricity control limits amount of cylindricity error
• Cylindricity feature requires no datum reference and modifiers
• Cylindricity feature controls the form of diameter of a perfect
cylinder

7. Angularity
• It is used to control the angle of the surface
• Angularity requires datum reference and an angle must be specified
between the tolerance feature and datum reference
• When angularity is applied to a plane, the tolerance zone will be two
parallel planes oriented by a basic angle and all the elements will lie
within the tolerance zone
• When angularity is applied to FOS, it controls the orientation of the
axis of FOS
• When diameter is specified before the angular tolerance value, it
indicates that the tolerance zone is cylindrical

8. Perpendicularity
• When the perpendicularity is applied to a surface, the tolerance zone
is two parallel planes which are 90 degree to the datum
• When the perpendicularity is applied to a planar FOS, its tolerance
zone is applied to both the surface of FOS
• When the perpendicularity control is applied to a planar surface, it
controls the orientation of flatness of the surface
• When the perpendicularity control is applied to a FOS, it control the
orientation of axis of the FOS
• If MMC is indicated with perpendicularity control, then bonus
tolerance is permissible
• When the diameter is specified before the tolerance value, then the
shape of the tolerance zone is cylindrical

9. Parallelism
• When parallelism is applied to a planar surface, the tolerance zone is
two parallel planes which are parallel to the datum plane.
• When parallelism is applied to a FOS, its tolerance zone is applied to
the axis or center plane of the FOS.
• When the diameter is specified before the tolerance value, then the
shape of the tolerance zone is cylindrical
• When the parallelism control contains a diameter symbol in front of
the tolerance value, the shape of tolerance value will be cylindrical
• The axis of the tolerance diameter must be within the tolerance zone
• the tolerance zone may float within the allowable location tolerance
zone

10. Position
• Tolerance of position (TOP)
• It is used to control the location of the FOS or a pattern of FOS
• True position is the theoretically exact location of a FOS
• TOP control is a geometric tolerance that defines the location tolerance of
FOS from its true position.
• Modifiers and datum references are used when TOP is used
• When Modifier is given for a part with TOP, then the tolerance is applied only
to that modifier condition
• When TOP is applied on MMC, bonus tolerance and datum shift is permitted

11. Concentricity
• It is the condition where the
mid points of all diametrically
opposed elements of a
surface of revolution are
congruent with the axis of a
datum feature.
• All the median points of the
tolerance diameter must be
within the tolerance zone.
• A concentricity control,
datum references are always
applied at RFS
• Concentricity requires datum
reference and must be
applied to a cylindrical FOS
and at RFS
• The tolerance zone for a
concentricity control is a
cylinder that is co axial with
the datum

12. Symmetry
• It is the condition where the median points of all opposed elements of two or
more feature surfaces are congruent with the datum axis or datum center
plane of a datum feature
• The symmetry control requires datum reference and it must be applied to a
planar FOS and RFS
• The symmetry tolerance value determines the size of tolerance zone
• The tolerance zone for a symmetry control is two parallel planes centered
about the datum center plane
• The distance between the plane is equal to the symmetry control tolerance
value
• Median points of tolerance feature must be within the tolerance zone

13. Profile of a line
• Profile of a line establishes a two-dimensional tolerance zone that
controls individual line elements of a feature or surface. Profile of a
line is usually applied to parts with varying cross-sections, or to
specific cross sections critical to a part's function.
• Profile control is a geometric tolerance which specifies a uniform
boundary along the true profile that elements of a surface must lie
within
• When a profile of a line control is specified the tolerance zone is two
uniform lines. The tolerance zone applies for each line element of the
surface
• It has 2D tolerance zone
• It can be used with the datum feature as a related feature control and
without a datum reference as a form control

14. Profile of a surface
• It is a powerful geometric tolerance which is used to control the part
surface
• It controls the size, location, orientation and form
• When the profile of a surface control is specified, tolerance zone is
uniform boundary. The boundary applies for the full length and width
of the surface
• It must have a datum reference and should be applied to a true
profile
• It has 3D tolerance zone and it can be used to tolerance a polygon,
conical feature

15. Circular Run out
• It is a composite control that affects the form, orientation, location of
circular elements of a part feature relative to a datum axis
• It is applied to each circular element of the tolerance feature independently
• Tolerance zone exist for each circular element of the tolerance diameter
• The shape of the tolerance zone is two co-axial circles whose centers are
located on the datum axis.
• It is known as composite control because it limits the circularity, orientation
and axis offset of a diameter.
• Circular run out tolerance zone is the radial distance between circles equal
to the run out tolerance value

16. Total Run out
• It is a composite control that affects the form, orientation, location of all
surface elements of a diameter relative to a datum axis
• Total run out requires a datum reference and it must be applied at RFS
• The run out tolerance value is equal to the radial distance between the
two cylinders
• The tolerance zone of a total run out is the two co-axial cylinders whose
centers are located on the datum axis
• It is also a composite control as it limits the location, orientation and
cylindricity

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