Straightness (⏤)
Straightness (⏤) is a form tolerance. A line on the surface, or the axis of the feature, may depart from a perfect straight line only by the amount given in the frame, and no datum is referenced.
Easily confused with
How to read it
The straightness symbol is a short horizontal line in the first compartment of a feature control frame, with the tolerance after it. In ASME Y14.5-2018, as Jaime Berez’s UNC Charlotte course notes set it out, straightness is one of the four form controls with Flatness (⏥), Circularity (○) and Cylindricity (⌭): it limits how far a line element of a surface, or a feature’s axis, departs from a perfect straight line, and it takes no datum. The UK National Physical Laboratory’s guide to ISO drawings gives the tolerance zone as two parallel lines the tolerance apart.
Where the frame points at the surface, each line element is checked on its own, independent of the others. Where the frame sits with a size dimension, Gene Cogorno’s GD&T course guide says the tolerance applies to the feature’s median line instead, and a circled M can then follow it.
Also searched as: ⏤, straightness gd&t, straightness 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.
Look-alikes
Next to Flatness (⏥), the difference is lines against a surface: straightness takes one line element at a time, flatness the whole face between two parallel planes. Unicode encodes the symbol as ⏤ (U+23E4) STRAIGHTNESS and notes the same character is the first form of the direct current symbol; the second direct current form is ⎓ (U+2393).
Read next
- Next in GD&T symbolsFlatness (⏥)Flatness (⏥) is a form tolerance: the whole surface has to lie between two parallel planes set the tolerance apart. It takes no datum.
- The same shape in Asian flagsFlag of JordanJordan’s flag has three equal stripes of black, white and green and a red triangle at the pole holding a white seven-pointed star. Al-Mamlaka, Jordan’s public broadcaster, explains the stripes as the Umayyad, Abbasid and Fatimid caliphates, the red triangle as the Hashemite family, and the seven points of the star as the seven verses of the Fatiha, the opening chapter of the Quran.
More GD&T symbols
The same shape elsewhere
Browse symbols drawn with lines.
Sources
- Fundamentals of Geometric Dimensioning and Tolerancing (GD&T), Part I, Jaime Berez, seminar adapted from an undergraduate mechanical engineering course, version 2.1.0, 2023, Center for Precision Metrology, University of North Carolina at Charlotte (Zenodo), Slides 27 and 29
- 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, Form tolerances
- 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, Chapter 5, Form, review answers
- Miscellaneous Technical, Range: 2300–23FF (code chart), The Unicode Standard, Unicode Consortium, U+23E4
Researched, edited and approved by Rory Hansen before publishing. Last reviewed October 9, 2026. How we research
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