POSITION

LOCATION

Controls where a feature is located relative to datums

⚠ DATUM REQUIREDASME Y14.5-2018 §7

Position is the most powerful and commonly used GD&T control. It defines a cylindrical (or other shaped) tolerance zone within which the axis, center plane, or center point of a feature must lie, relative to the datum reference frame. All locating dimensions must be basic (boxed).

WHEN TO USE IT

Use position to locate holes, slots, bosses, pins, or any feature of size relative to a datum reference frame. It is the correct control for bolt patterns, clearance holes, and any feature where both location and orientation must be controlled simultaneously.

COMMON MISTAKES

Using ± coordinate dimensions instead of basic dimensions to locate the feature

Omitting the datum reference — position always requires datums

Using the wrong datum reference order — primary datum controls the most degrees of freedom

Applying position to a surface instead of a feature of size — use profile for surfaces

Forgetting MMC or LMC modifiers on clearance holes where bonus tolerance would benefit manufacturing

IS YOUR CALLOUT CORRECT?

Check these before releasing your drawing.

Are all locating dimensions basic (boxed)?

Position requires basic dimensions for true position. ± dimensions cannot be used.

Does the FCF include the correct datum references in the right order?

Primary datum first, then secondary, then tertiary. Order matters — it defines the constraint sequence.

Is the feature a feature of size (hole, slot, boss) rather than a surface?

Position applies to features of size. For surfaces, use profile of a surface instead.

RELATED SYMBOLS

OTHER LOCATION CONTROLS

◎Concentricity ⌯Symmetry

Redprint checks position automatically

Redprint checks for missing basic dimensions, incorrect datum order, missing datum references, and flags features of size that have only ± tolerances with no position control.

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