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.