Concentricity controls the derived median points of a cylindrical feature relative to a datum axis. It addresses the feature's median geometry, not simply the runout of its surface. The illustrated callout is a legacy ASME example, removed from Y14.5-2018.
Datum required
Yes
MMC / LMC applicable
No — legacy median-point control
Control type
Location · legacy ASME
What it controls
Derived median points relative to a datum axis
Typical features
Older stepped shafts and coaxial bores
INTERACTIVE APPLICATION
GD&T concentricity example: stepped shaft
Datum cylinder A and controlled cylinder, viewed from the side.
NO CONCENTRICITY CONTROL
Size checks can pass while median points vary
Datum cylinder establishes axis A.
The controlled cylinder can meet its size limits.
Its derived median points may still drift relative to A.
Limitations
Size alone does not state the required coaxial relationship.
Misalignment can affect fit or rotation where coaxiality matters.
A surface runout check does not define the legacy median-point requirement.
CONCENTRICITY CONTROL
Median points controlled to datum axis A
Illustrative legacy frame: ◎ | ⌀0.10 | A.
Derived median points stay inside the specified zone along the feature.
Interpret the callout using the standard edition on the drawing.
Advantages
States a median-point relationship to datum A explicitly on legacy drawings.
Can express specialist coaxial design intent.
Inspection is demanding; position or runout often communicates the function more directly on new drawings.
01 / DRAWING
How is Concentricity used?
Establish datum axis A from the specified datum cylinder. Attach the legacy concentricity frame to the controlled cylinder's size dimension. The derived median points along its length must stay within the stated cylindrical tolerance zone around A; a single end view cannot establish this full-length relationship.
Stepped-shaft drawing exampledatum cylinder A and controlled cylinder
◎⌀0.10A
Illustrative legacy ASME frame
Illustrative legacy frame: derived median points of the controlled cylinder lie inside a ⌀0.10 mm zone coaxial with datum A.
Applying the callout
Identify the datum cylinder and establish its axis A. Attach the frame to the controlled cylindrical feature. Evaluate derived median points at sections along the controlled length—not just one visible end centre.
How to read a concentricity tolerance
Read the concentricity symbol, then the diametral zone size (⌀0.10 mm here), followed by datum A. The zone is centred on A. Check the drawing’s standard and edition before interpreting any modifier or inspection rule.
CHOOSING A CONTROL
Concentricity vs position and runout
Position
Choose position when the functional requirement is to locate a feature’s axis relative to datums. It controls the derived axis in its position zone.
Runout
Choose circular or total runout when the rotating surface’s variation relative to a datum axis is the functional concern. An indicator check of surface runout does not establish legacy median-point concentricity.
02 / VALUES
Commonly defined variable values
These are illustrative values seen on legacy-style coaxial features, not preferred values for new drawings. Choose a control and tolerance from the actual function and inspection plan.
Scroll the table sideways to see every column.
Illustrative concentricity tolerances for early design discussion
Application
Illustrative starting value
Example feature
Notes / caution
Legacy stepped shaft
⌀0.05–0.15 mm
Ø30/Ø50 mm shaft
Use only when required by stated legacy edition.
Coaxial bore pair
⌀0.05–0.20 mm
Bearing housing
Check full-length datum-axis construction.
Rotating journal
⌀0.02–0.10 mm
Motor shaft
Runout may better match functional need.
These are planning examples, not universal rules or guaranteed process capabilities. Set the actual tolerance from function, size, length, process capability, inspection method and the standard specified on the drawing.
03 / INSPECTION
How is concentricity measured in real life?
Establish datum axis A, then compare measured derived median points along the controlled cylinder with the specified tolerance zone.
CMM: probe several sections and evaluate their median points relative to A.
Roundness or form equipment: measure cross-sections where the setup supports the drawing requirement.
Specialist setup: use when datum simulation or access needs a tailored method.
This can be harder and more expensive to verify than position or runout. A runout check alone does not verify a legacy concentricity callout.
Example setup: section median points compared with datum axis A.
ASME Y14.5-2018 (R2024) — legacy control
This is a legacy ASME control removed in the 2018 edition. Interpret older drawings using their stated edition; select position, profile or runout for new requirements as appropriate to function.
