What is the classification of form and position tolerance and what are the prescribed elements?

The shape tolerance zone includes the shape, direction, position and size of the tolerance zone.

Shape tolerance can be divided into three categories according to its characteristics: shape tolerance, position tolerance and shape or position tolerance.

Shape tolerance includes straightness, flatness, roundness, cylindricity, etc. Position tolerance is divided into azimuth tolerance, positioning tolerance and runout tolerance, including parallelism, verticality, inclination, position, coaxiality (concentricity) and symmetry. Shape or position tolerance includes straight line profile, surface profile, etc.

Shape and position tolerance bullets

Straightness: This symbol is a short horizontal line (-), which is an index to limit the deviation between the actual straight line and the ideal straight line. This is a requirement for straightness.

Flatness: the symbol is parallelogram, which is an index to limit the deviation between the actual plane and the ideal plane. It is the requirement of uneven plane.

Roundness: The symbol is circle (○), which is an index to limit the deviation between the actual circle and the ideal circle. It is a requirement for the circular outline of parts with cylindrical surfaces (including conical surfaces and spherical surfaces) on the normal section (the surface perpendicular to the axis).

Cylindricity: The symbol is a circle (/○/) sandwiched between two oblique lines, which is an index to limit the variation between the actual cylindrical surface and the ideal cylindrical surface. Control various shape errors of cylinder section and shaft section, such as roundness, element line straightness, axis straightness, etc. Cylindricity is a comprehensive index of various shape errors of cylinders.

Line profile: The symbol of convex curve (⌒) is an index to limit the deviation between actual curve and ideal curve. This is the requirement for the shape accuracy of non-circular curves.

Surface profile: this symbol is semi-circular in shape and horizontal in bottom, which is an index to limit the change of actual surface to ideal surface and a requirement for surface shape accuracy.