Datum targets identify selected points, lines or small areas used to establish a datum. They are useful when full-surface contact would be unstable or impractical, such as a rough casting or a large formed panel.
Datum required
No datum reference inside the target symbol
MMC / LMC applicable
No — target identifier
Control type
Reference establishment
What it controls
Specified contact points, lines or areas
Typical features
Cast pads, rough faces and formed panels
INTERACTIVE APPLICATION
Datum Target: drawing and interpretation
DRAWING CALLOUT
Read the annotation
A1, A2 and A3 are three contact areas establishing datum A. The upper ⌀8 states each circular target area’s diameter. It is not a geometric tolerance. A point target has no area-size value.
Key points
A target is a specified contact location on a datum feature. Several targets with the same datum letter work together to establish that datum.
INTERPRETATION
Connect the callout to the part
Targets contributing to datum A.
Practical caution
Target location, contact size and support conditions matter. Three non-collinear contacts can establish a primary plane; the full datum system may need additional targets.
01 / PURPOSE
Why use this annotation?
Make the fixture and inspection contact repeatable without relying on every irregular point of a large surface.
02 / APPLICATION
Where is it applied?
Castings, forgings, sheet-metal parts and components supported at selected pads.
03 / DRAWING
Five ways to specify datum contact
Point, line and area targets identify the contacts that a fixture or inspection setup must reproduce. Example dimensions are in millimetres.
Point and line targets
An X identifies point contact; a phantom line identifies line contact. Both identifiers have blank upper compartments.
Circular area
The hatched pad is ⌀8; the upper compartment specifies its diameter.
Rectangular area
Outline dimensions 12 × 8 define the contact pad; locate its centre with basic dimensions.
Square area
An 8 × 8 contact pad is identified and located independently of the part size.
Indication, identification and location
The drawing marks the intended contact and connects it to a divided circular identifier. The lower compartment gives the datum letter and target number. Basic dimensions locate the contact.
Points and lines
Use an X for a point and a phantom line for line contact. Leave the identifier’s upper half blank; specify line extent separately when needed.
Contact areas
Hatching identifies the pad. A circular area uses a diameter; non-circular pads need their complete outline dimensions. These numbers specify contact size, not geometric tolerance.
Near and far contacts
A solid connecting line identifies a visible-side target; a dashed connecting line identifies a far-side target in this ASME-style convention.
Common mistake
A1 through A5 here are separate examples, not a required five-contact setup. Select the contacts and datum precedence from the part’s function and governing standard.
04 / VALUES
Example values and identifiers
These explain the drawing notation. They are examples, not recommended default tolerances.
Targets contributing to datum A.
Diameter of the indicated circular target area.
Point target; no target-area size is stated.
05 / INSPECTION
Checking the requirement in practice
Support the part at the specified target locations with the intended contact shape. A fixture or CMM can establish the reference from those targets. Do not replace selected targets with whole-surface alignment.
Choose sampling, fixtures and acceptance rules that suit the feature and the drawing’s cited standard.
ASME Y14.5-2018 (R2024)
ASME Y14.5 datum targets identify controlled contact locations; their size and number matter.
