Free reference
GD&T symbols
The GD&T symbol reference draws and explains, in a sentence each, the geometric characteristics of ASME Y14.5 and ISO 1101 (form, profile, orientation, location and runout), their modifiers, and the dimensioning and datum symbols that go with them, searchable and ready to copy; its reader explains a feature control frame typed as text, box by box and aloud.
41 symbols, by category.
Form
The shape of a single feature on its own, never related to a datum.
Straightness
Form · No datums
Each line element of a surface must lie between two parallel lines the tolerance apart; with ⌀ before the tolerance, the feature's axis must lie within a cylinder of that diameter.
⏤U+23E4
Flatness
Form · No datums
The whole surface must lie between two parallel planes the tolerance apart.
⏥U+23E5
Circularity
Form · No datums · also called roundness
Each circular cross-section must lie between two concentric circles whose radii differ by the tolerance.
○U+25CB
Cylindricity
Form · No datums
The whole cylindrical surface must lie between two coaxial cylinders whose radii differ by the tolerance.
⌭U+232D
Profile
A surface or line against its true profile; with datums it also orients and locates it.
Profile of a line
Profile · Datums optional · also called line profile
Each line element of the surface, cross-section by cross-section, must lie within a band of the tolerance's width around its true profile.
⌒U+2312
Profile of a surface
Profile · Datums optional · also called surface profile
The whole surface must lie within a zone of uniform width around its true profile, which basic dimensions define; with datums it also controls the surface's orientation and location.
⌓U+2313
Orientation
The angle of a feature to a datum: always related to one.
Angularity
Orientation · Needs a datum
The surface, axis or center plane must lie within a zone at the stated basic angle to the datum.
∠U+2220
Perpendicularity
Orientation · Needs a datum · also called squareness
The surface, axis or center plane must lie within a zone at exactly 90° to the datum.
⟂U+27C2
Parallelism
Orientation · Needs a datum
The surface, axis or center plane must lie within a zone parallel to the datum.
∥U+2225
Location
Where a feature sits, from its datums.
Position
Location · Usually with datums · also called true position, TP
The feature's axis, center plane or center point must lie within a zone around its true position, which basic dimensions locate from the datums.
⌖U+2316
Concentricity
Location · Needs a datum · also called coaxiality
The median points of the feature must lie within a cylinder of the tolerance's diameter around the datum axis. ASME Y14.5 removed it in 2018 in favor of position, runout or profile; ISO 1101 keeps the symbol, for concentricity of a point and coaxiality of an axis.
In ISO 1101 and ASME Y14.5 before 2018.
◎U+25CE
Symmetry
Location · Needs a datum
The median points of the feature must lie between two parallel planes centered on the datum center plane, the tolerance apart. ASME Y14.5 removed it in 2018 in favor of position or profile; ISO 1101 keeps it.
In ISO 1101 and ASME Y14.5 before 2018.
⌯U+232F
Runout
A surface as the part turns about a datum axis.
Circular runout
Runout · Needs a datum · also called runout
Each circular element of the surface must stay within the tolerance, read as the full movement of an indicator, while the part turns 360° about the datum axis.
↗U+2197
Total runout
Runout · Needs a datum
The whole surface must stay within the tolerance, read as the full movement of an indicator, while the part turns about the datum axis and the indicator travels along the surface.
⌰U+2330
Modifiers
Letters and marks in a feature control frame that change how its tolerance applies.
Maximum material condition (MMC)
Modifier · also called MMC, bonus tolerance
The tolerance applies when the feature holds the most material - the smallest hole, the largest pin - and grows by as much as the feature departs from that size: the bonus tolerance.
ⓂU+24C2
Least material condition (LMC)
Modifier · also called LMC
The tolerance applies when the feature holds the least material - the largest hole, the smallest pin - and grows by as much as the feature departs from that size.
ⓁU+24C1
Regardless of feature size (RFS)
Modifier · also called RFS
The tolerance stays the same at any size of the feature. Current ASME Y14.5 applies it by default where no modifier is shown, so the symbol appears mainly on older drawings.
In Older drawings; current ASME Y14.5 applies it by default, without the symbol.
ⓈU+24C8
Projected tolerance zone
Modifier
The tolerance zone extends beyond the part, out of the hole, by the stated height: used where a bolt or pin will stand out of a threaded or press-fit hole.
ⓅU+24C5
Free state
Modifier
The tolerance applies to a flexible part as it lies, unrestrained, rather than held in its assembled shape.
ⒻU+24BB
Tangent plane
Modifier
The tolerance applies to the plane touching the surface's high points, not to every point of the surface.
ⓉU+24C9
Unequally disposed profile
Modifier
The profile zone sits unevenly about the true profile: the value after Ⓤ is how much of the zone lies on the side that adds material.
In ASME Y14.5, 2009 and later.
ⓊU+24CA
Statistical tolerance
Modifier · also called ST
The tolerance was set by statistical tolerancing, so the parts are to be made under the statistical process control it assumes.
In ASME Y14.5.
ST
Continuous feature
Modifier · also called CF
A group of interrupted features, such as a bore broken by grooves, is treated as one continuous feature.
In ASME Y14.5, 2009 and later.
CF
Dimensioning symbols
Symbols that say what kind of dimension a number is.
Diameter
Dimensioning symbol
The number after it is a diameter; in a feature control frame, the tolerance zone is a cylinder or circle of that diameter.
⌀U+2300
Spherical diameter
Dimensioning symbol
The number after it is the diameter of a sphere; in a feature control frame, the tolerance zone is a sphere.
S⌀S + U+2300
Radius
Dimensioning symbol
The number after it is a radius.
R
Spherical radius
Dimensioning symbol
The number after it is the radius of a sphere.
SR
Controlled radius
Dimensioning symbol
A radius whose arc must be a fair curve, with no flats or reversals, inside its size limits.
CR
Square
Dimensioning symbol
The feature is square; the number after it is the length of a side.
□U+25A1
Counterbore or spotface
Dimensioning symbol · also called spotface, SF
A flat-bottomed enlargement at the mouth of a hole, given as a diameter and a depth; with SF inside the symbol, a spotface, which only cleans up the surface.
⌴U+2334
Countersink
Dimensioning symbol
A cone-shaped enlargement at the mouth of a hole, given as a diameter and an included angle.
⌵U+2335
Depth
Dimensioning symbol · also called deep
The number after it is a depth: of a hole, a counterbore or a thread.
↧U+21A7
Between
Dimensioning symbol
The tolerance applies between the two points named, as in A ↔ B, usually to a profile.
↔U+2194
All around
Dimensioning symbol
A circle where the leader bends: the tolerance, usually a profile, applies all the way around the outline in that view.
All over
Dimensioning symbol
Two circles where the leader bends: the tolerance, usually a profile, applies to every surface of the part.
In ASME Y14.5, 2009 and later.
Basic dimension
Dimensioning symbol · also called theoretically exact dimension, TED, boxed dimension
A number in a box is exact and theoretical, with no tolerance of its own: it locates or shapes a tolerance zone, and the feature control frame says how far the feature may stray.
Reference dimension
Dimensioning symbol · also called REF
A number in parentheses is for information only: it is not a requirement and is not inspected.
( )
Number of places
Dimensioning symbol · also called times, X
A number and an X before a callout, as in 4X, means it applies to that many identical features.
4X
Arc length
Dimensioning symbol
An arc over a number means the dimension is measured along the arc, not straight across.
⌒U+2312
Datums
How a drawing names the features its tolerances are measured from.
Datum feature
Datum symbol
A capital letter in a box, attached to a feature by a triangle, names that feature as a datum: the reference that feature control frames measure from.
Datum target
Datum symbol
A circle divided across the middle, with the target's size above and the datum letter and target number below (A1): a point, line or area where the part touches its setup.
No symbol matches that. Try a name, such as position, or a word from its meaning.
How to read it
How to read a feature control frame.
A geometric tolerance is written in a row of boxes, the feature control frame, read left to right.
- The characteristic. What is controlled: here position, ⌖.
- The tolerance. The size of the zone the feature must stay within. ⌀ in front makes the zone a cylinder (or a circle); a modifier after it, here Ⓜ for maximum material condition, says how the tolerance applies.
- The primary datum. A: the part is set on this feature first.
- The secondary datum. B: then against this one.
- The tertiary datum. C: then against this one, which fixes the part completely.
Read aloud, the frame says: the axis of this hole must lie within a cylinder 0.25 in diameter, at maximum material condition, centered on its true position, which basic dimensions locate from datums A, B and C. A frame for a form tolerance, such as flatness, has only the first two boxes, because form needs no datum.
Sources: ASME Y14.5-2018 (Dimensioning and Tolerancing) and ISO 1101 (geometrical tolerancing). Where the two differ, each card says which carries the symbol.
Feature control frame reader
Read a feature control frame.
Type or paste a frame, box by box: the symbol or its name, the tolerance with its modifiers, then the datums. It reads each box, then the whole frame aloud, and says where a frame breaks a rule of the standard.
Position
The frame ⌖ | ⌀0.25 Ⓜ | A | B | C
Read aloud: The feature's axis must lie within a cylinder 0.25 in diameter, centered on its true position, which basic dimensions locate from datums A, B and C, at maximum material condition, growing as the feature departs from it.
⌖Characteristic- Position: The feature's axis, center plane or center point must lie within a zone around its true position, which basic dimensions locate from the datums.
⌀0.25 ⓂTolerance- The tolerance zone is a cylinder 0.25 in diameter, in the drawing's units; Ⓜ: it applies at maximum material condition and grows by as much as the feature departs from that size.
APrimary datum- Datum A: the part is set on this datum feature first.
BSecondary datum- Datum B: then against this one.
CTertiary datum- Datum C: then against this one, which fixes the part completely.
Questions
What people ask about GD&T symbols.
What are the 14 GD&T symbols?
The 14 geometric characteristics are straightness, flatness, circularity and cylindricity (form); profile of a line and profile of a surface (profile); angularity, perpendicularity and parallelism (orientation); position, concentricity and symmetry (location); and circular runout and total runout (runout). ASME Y14.5 removed concentricity and symmetry in 2018, leaving 12; ISO 1101 keeps all 14.
What does ⌖ mean in GD&T?
It is position, often called true position. The feature's axis, center plane or center point must lie within a zone around its true position, which basic dimensions locate from the datums.
What is MMC in GD&T?
Maximum material condition, written Ⓜ after the tolerance. The tolerance applies when the feature holds the most material - the smallest hole, the largest pin - and grows by as much as the feature departs from that size: the bonus tolerance. For a hole of 10.0 to 10.2 mm with a position tolerance of ⌀0.1 at MMC, the zone is ⌀0.1 when the hole is 10.0 and grows to ⌀0.3 when it is 10.2.
Which GD&T symbols need a datum?
Orientation (angularity, perpendicularity and parallelism), runout, concentricity and symmetry always do, and position nearly always does. Profile may use datums or not. Form tolerances (straightness, flatness, circularity and cylindricity) never use one.
How do you type GD&T symbols?
Most have a Unicode character, such as ⌖ (U+2316) for position and ⏥ (U+23E5) for flatness: copy them from the cards on this page. Few fonts draw them all, so on a drawing a CAD program's GD&T font or symbol menu is more reliable.
What is the difference between ASME Y14.5 and ISO 1101 symbols?
The shared characteristics use the same symbols. ASME Y14.5 removed concentricity and symmetry in 2018, while ISO 1101 keeps them. The bigger difference is a default: ASME applies Rule #1, the envelope requirement, to features of size, while ISO applies the independency principle of ISO 8015 unless the drawing says otherwise.
From SpecCapture
Reading a whole drawing?
Feature control frames sit on the drawing's views; the data around them - the title block, its general tolerances, the revision history and the notes - is what SpecCapture reads. SpecCapture reads the title block, the revision history, the bill of materials, the hole table, the application block, the tabulated dash numbers and the general notes off 2D engineering drawings, with a box on the drawing around every value it reads, so checking it takes a glance.