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GD&T Symbols

 

Symbols in GD&T

  • GD&T has 14 geometric characteristic symbols.
  • Various symbols used to specify tolerance zones are given below
    • Form
    • Position
    • Profile
    • Orientation
    • Runout

 

 

 

Straightness

Straightness describes a condition where an element of a surface or an axis is a straight line.

 

 

 

Flatness

Flatness is the condition of a surface having all elements in one plane.

 

The surface must lie between two planes 0.25 mm apart

 

 

Circularity

Circularity describes the condition on a surface of revolution (cylinder, cone, or sphere) where all points of the surface intersected by any plane (1) perpendicular to a common axis (cylinder, cone), or (2) passing through a common centre (sphere) are equidistant from the centre.

 

Each circular element of the surface in a plane perpendicular to the axis must lie between two concentric circles, one having a radius 0.25 mm larger than the other

 

 

Cylindricity

Cylindricity describes a condition of a surface of revolution in which all points of a surface are equidistant from a common axis.

 

The cylindrical surface must lie between two concentric cylinders one with a radius 0.25 mm larger than the other

 

 

Parallelism

Parallelism is the condition of a surface, line, or axis, which is equidistant at all, points from a datum plane or axis.

 

1. The surface must lie between two parallel planes 0.12 mm apart, which are parallel to datum plane A.

2. The feature axis must lie within a 0.2 mm dia. of cylindrical zone parallel to datum axis A.

 

 

 

Perpendicularity

Perpendicularity is the condition of a surface, axis, or line, which is 90 deg. from a datum plane or a datum axis.

 

The feature axis must lie between two parallel planes 0.2 mm apart, perpendicular to datum axis A

 

 

Angularity

Angularity is the condition of a surface, axis, or centre plane, which is at a specified angle (other than 0Ëš, 90Ëš, 180Ëš or 270Ëš) from a datum plane or axis.

 

The surface must lie between two parallel planes 0.4 mm apart inclined at an angle of 300 to datum plane A

 

 

Profile of a surface

Profile of a surface is the condition permitting a uniform amount of profile variation, either unilaterally or bilaterally, on a surface.

 

 

 

 

Profile of a line

Profile of a line is the condition permitting a uniform amount of profile variation, either unilaterally or bilaterally, along a line element of a feature.