Concentricity (◎)
Concentricity (◎) required the median points of a round feature to lie within a cylindrical zone around a datum axis. ASME Y14.5-2018 removed it from the US standard; ISO 1101 still has a concentricity and coaxiality symbol, with a different meaning.
Easily confused with
- Circularity (○)Circularity (○), also called roundness, is a form tolerance: each circular cross-section of the feature has to lie between two concentric circles the tolerance apart. It takes no datum.
- Position (⌖)Position (⌖), often called true position, controls where a feature of size such as a hole, pin or slot sits: its axis or centre plane has to lie in a zone centred on the exact location given by basic dimensions from the datums.
How to read it
The symbol is two concentric circles. Under ASME Y14.5-2009, as Mitutoyo’s Jim Salsbury quotes it, concentricity was the condition where the median points of all diametrically opposed elements of a surface of revolution are congruent with a datum axis. Cogorno’s guide describes it as a location control with a cylindrical tolerance zone coaxial with the datum axis, applying only regardless of feature size.
Also searched as: ◎, concentricity gd&t, concentricity symbol.
This explains what a symbol specifies on a drawing. It isn't inspection or design guidance; the drawing and the edition of the standard it cites take precedence.
Removed from ASME Y14.5 in 2018
ASME Y14.5-2018 removed concentricity and symmetry, “term, symbol, and concept” (paragraph A-8.4, as Salsbury quotes it), to “eliminate the confusion that surrounds these symbols and their misapplication”. Salsbury adds that many organizations had banned them decades earlier. NIST and UNC Charlotte’s seminar notes give the reason in plain terms, that the GD&T definition was complex and often misunderstood and differed from the everyday meaning, and say what replaces it: Position (⌖) for the axis (“coaxiality”) and runout for the surface’s wobble. The symbol still appears on drawings made to the 2009 or earlier editions, which Cogorno’s guide notes many readers are still required to read.
Concentricity in ISO 1101
ISO drawings keep a symbol of the same shape. The National Physical Laboratory’s guide reads it as concentricity when it relates the centre points of two circles and as coaxiality when it relates the axes of two cylinders. Salsbury sets the two systems side by side: in ISO 1101 concentricity is a 2D control of a centre point and coaxiality a 3D control of the derived median line, both forms of position. His summary of the clash: same symbol, different meaning, with ISO controlling the axis and ASME the opposed median points.
Look-alikes
Circularity ○ is a single circle and controls roundness only. Position ⌖ is a circle with a cross. The two-circle shape is the character ◎ (U+25CE), which Unicode names BULLSEYE.
Read next
- Next in GD&T symbolsSymmetry (⌯)Symmetry (⌯) required the median points between two opposed surfaces, such as the two sides of a slot, to lie between two parallel planes centred on a datum. ASME Y14.5-2018 removed it from the US standard; ISO drawings still use it.
- The same shape in Emoji meaningsFace holding back tears 🥹A face with big eyes welling up with tears and a small smile. It is used for being moved: proud, grateful or touched, and sometimes sad or angry and trying not to show it.
More GD&T symbols
The same shape elsewhere
Browse symbols drawn with circles.
Sources
- GD&T and the new ASME Y14.5-2018, Jim Salsbury, Mitutoyo Institute of Metrology, presentation, 2019, Mitutoyo America Corporation, Slides on ASME Y14.5-2018 changes and ISO 1101
- Fundamentals of Geometric Dimensioning and Tolerancing (GD&T), Part II, Jaime Berez (UNC Charlotte) and Maxwell Praniewicz (NIST), seminar slides, National Institute of Standards and Technology, Slide 5
- Geometric Dimensioning and Tolerancing for Mechanical Design: Instructors’ Guide, Gene R. Cogorno, guide to the McGraw-Hill textbook, rev. 10/12/2020, Technical Training Consultants, Appendix A, Concentricity and Symmetry
- Fundamental Good Practice in the Design and Interpretation of Engineering Drawings for Measurement Processes, Measurement Good Practice Guide No. 79, David Flack and Keith Bevan, 2005, National Physical Laboratory (UK), Chapter 4, Concentricity/co-axiality
- Geometric Shapes: Range 25A0–25FF (code chart), The Unicode Standard, Version 18.0, Unicode Consortium, U+25CE
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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