GD&T quick reference

GD&T symbol quick reference per ASME Y14.5: form, orientation, location, profile and runout controls, with what each one controls and whether it needs a datum.

GD&T quick reference

The 12 characteristic symbols in ASME Y14.5-2018 and the modifiers that show up in real feature control frames. Concentricity and symmetry were removed in the 2018 revision; use position or profile instead.

⏤

StraightnessForm · datum no

A line element or axis stays within a tolerance zone. Cheap way to control a shaft that must slide.

⏥

FlatnessForm · datum no

The whole surface lies between two parallel planes. Use it on gasket faces and mounting pads.

○

CircularityForm · datum no

Each cross-section is round within a band. Independent of size.

⌭

CylindricityForm · datum no

Roundness, straightness, and taper all at once. Expensive to inspect; use it only where a bearing or seal needs it.

⌒

Profile of a lineProfile · datum optional

A 2D cross-section follows the true shape within a band.

⌓

Profile of a surfaceProfile · datum optional

3D surface follows the model within a band. The workhorse for cast, molded, and scanned parts.

∠

AngularityOrientation · datum yes

Surface or axis held at a basic angle to a datum.

⟂

PerpendicularityOrientation · datum yes

Square to a datum within a band. Common on bosses and bored holes.

∥

ParallelismOrientation · datum yes

Parallel to a datum within a band. Does not control location.

⌖

PositionLocation · datum yes

Where a hole, slot, or boss axis is allowed to be. With Ⓜ it gives bonus tolerance as the hole grows; this is what makes bolt patterns work.

↗

Circular runoutRunout · datum yes

Wobble of each circular element as the part spins on a datum axis.

⌰

Total runoutRunout · datum yes

Wobble of the whole surface as it spins. Controls taper too.

Modifiers

ⓂMaximum material condition. Tolerance grows as the feature departs from MMC. Use for clearance holes and gauging.

ⓁLeast material condition. Use when wall thickness or edge distance is what matters.

ⓅProjected tolerance zone. Extends position control above the surface so a stud or press-fit pin lines up with the mating part.

ⒻFree state. Applies to flexible parts measured without restraint.

ⓉTangent plane. Only the high points of the surface count.

ⓊUnequally disposed profile. Puts more of the band on one side of the surface.

(ST)Statistical tolerance. Flags dimensions that assume process control (pairs with RSS stack-ups).

CFContinuous feature. Treats interrupted surfaces as one feature.

A reminder, not a substitute for the standard. If a drawing you received uses these in ways that do not make sense, that is usually the drawing, not you. I do drawing reviews.

More in Tolerancing & GD&T: Tolerance stack-up (1D), True position calculator, Go / no-go gauge sizes

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GD&T quick reference