Definition
Cylindricity is a geometric tolerance that controls the combined roundness and straightness of a cylindrical feature over its entire length, without reference to any datum.
What it means for the calculation
A tight cylindricity requirement on a shaft or bore usually needs grinding or a finishing pass after turning, since plain turning can leave taper or lobing within a coarser tolerance than cylindricity allows.
Where it appears on the drawing
In a feature control frame with the ⌭ symbol and a tolerance value; no datum reference is used, since cylindricity only controls the feature's own form relative to itself.
Common mistakes
Confusing cylindricity with a diameter tolerance (cylindricity constrains shape, not size) or with circularity (cylindricity covers the whole length, circularity only a single cross-section).
A tight cylindricity requirement on a shaft or bore usually needs grinding or a finishing pass after turning, since plain turning can leave taper or lobing within a coarser tolerance than cylindricity allows.
See how Blake reviews a partFrequently asked questions
Does cylindricity include roundness?
Yes, cylindricity combines roundness and straightness into a single tolerance for the whole cylindrical surface.
Why does cylindricity have no datum?
Because it only controls the feature's own form, not its relationship to another feature.
Can a part pass its diameter tolerance but fail cylindricity?
Yes, a shaft can measure the correct diameter at every cross-section yet still be tapered, oval or bent along its length, which fails cylindricity even though individual diameter checks pass.