Cylindricity is a GD&T form control that keeps an entire cylindrical surface between two coaxial cylinders whose radii differ by the tolerance. It limits roundness, straightness of the sides and taper in one callout, and it never uses a datum.
Cylindricity is the strictest form control for a diameter. Where circularity looks at slices and straightness looks at lines, cylindricity judges every point of the surface against one pair of perfect, coaxial cylinders. A shaft that is round in every slice but tapers, bows or bulges in the middle fails it.
It is used on precision journals, hydraulic spools and bores, pistons and press-fit pins, where the mating part touches the whole length and any taper or barrel shape changes the fit.
Because it is hard and slow to measure, cylindricity should be specified only where function needs it. Often circularity plus the size limits is enough.
The tolerance zone is the space between two coaxial cylinders whose radii differ by the tolerance value. All points of the surface must fall between them.
The cylinders may sit at any size and any orientation; only the shape of the surface counts. Like circularity, the value is radial.
Cylindricity never references a datum. If the diameter must also run true to another feature, add total runout or position.
| Modifier | With cylindricity |
|---|---|
| MMC or LMC | Not allowed. Cylindricity applies to the surface, never to the axis. |
| Free state | Can be used for non-rigid tubes or sleeves measured unrestrained. |
Example: a Ø20 mm hydraulic spool land, 40 mm long, with a cylindricity of 0.01 mm
Result: 0.007 mm is within 0.01 mm, so the land passes. Note that the taper alone used almost half of the tolerance.
Every GD&T symbol page: GD&T symbols chart
A circle with two parallel slanted lines touching it on opposite sides, like a cylinder seen from an angle.
No. It is a form control and is checked against a pair of floating coaxial cylinders.
Not quite. It covers both, plus taper and barrel shape between sections, judged against one common pair of cylinders.
No. It applies to the surface, not the axis, so material condition modifiers are not allowed.
Best on a roundness machine with a vertical column or a CMM scan, fitting two coaxial minimum-zone cylinders to many sections and lines.
COPLAIN AI PLATFORM
Coplain turns your cylindricity method (sections, fixturing and data handling) into a repeatable inspection job aid.
Generate yours automatically with Coplain →Related Tools & Templates