SMLease Design

Mechanical Product Design & Development Partner

Straightness : GD&T Tips SMLease Design


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

Where Straightness is Used

  • Used to control the foam of a line on the surface /  feature
  • Straightness of an axis

No Datum plane is required to define straightness and while defining axis straightness LMC and MMC modifiers can be used

Surface Straightness

It is a 2-Dimensional tolerance which is used to ensure that a part is uniform across a surface or feature. Straightness can be applied to a flat surface of a cylinder or block


Representation Of Surface Straightness

Tolerance Zone For Surface Straightness

Tolerance Zone will be 2 parallel lines 0.1 mm apart in 2D Plane

Measurement Of Surface Straightness


  • Dial Gauge is used to measure the value of straightness of a block or cylinder.
  • To measure the straightness part is moved in a straight line over the surface plate and variation in the reading of dial gauge is observed



Straightness of an Axis

  • Straightness of an axis controls the central axis of any part that defines how the axis of any part can deviate from straightness.
  • Axis Straightness tolerance makes a 3D tolerance zone.
  • It helps in controlling the bending or twisting of a part.
  • While defining axis straightness LMC and MMC modifiers can be used.

Representation Of Surface Straightness


Tolerance Zone for straightness of an Axis

Tolerance Zone will be a cylindrical boundary around the true central axis of the part.

Related Articles






Profile of a Surface Control

Profile Of a Line Control






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