What it controls
Cylindricity is a comprehensive form control for a cylinder. The whole surface must sit between two coaxial cylinders separated by the stated tolerance. The entire cylindrical surface: its roundness, straightness, and taper together.
The tolerance zone
How the zone works
The entire actual cylindrical surface must lie between two coaxial cylinders separated by the tolerance. Unlike circularity, the zone applies across the full controlled length at the same time.
Example drawing
See Cylindricity on a drawing
Tolerance zone visualized
See the tolerance zone in context
The complete cylinder, not a single slice
Cylindricity combines several form effects into one requirement: local roundness, longitudinal straightness, and taper of the cylindrical surface. It is still a form control, so the coaxial zone is free to orient and locate itself to best fit the actual surface.
Example feature control frame
The indicated cylindrical surface must remain within a 0.20 mm cylindrical zone over its complete controlled length.
Practical use
When to use Cylindricity
Use cylindricity for critical journals, precision bores, or sealing diameters when the complete surface must function as a cylinder—not merely be round at individual sections.
Inspection
How it is usually measured
A CMM, roundness/cylindricity instrument, or scanning system can sample the complete surface and compute the best-fitting coaxial boundaries. An indicator at one or two locations is not enough: it may miss taper or a local lobe elsewhere on the diameter.
Common mix-up
It is more demanding to make and inspect than circularity, so use it only when the whole surface function requires it.
Keep exploring
Straightness
Flatness
Circularity
Profile of a Line
Profile of a Surface
Angularity
Perpendicularity
Parallelism
Position
Circular Runout
Total Runout
Concentricity
Symmetry