GD&T Symbol Guide
Datum Target
Identifies a specific point, line, or area used to establish a datum from controlled contact locations.
Definition
A datum target defines a specific point, line, or area used to establish a datum on a part.
The target symbol is divided horizontally, with the datum letter and target number shown in the lower half.
Application
Use datum targets for castings, forgings, molded parts, or irregular surfaces where full-surface contact would be unstable or unrealistic.
Targets can represent points, lines, or defined areas depending on how the datum simulator should touch the part.
Target Points Establishing Datum A
Datum targets are numbered contact locations used when a full surface is not suitable as the datum simulator.
3D Tolerance Zone
Datum targets do not create tolerance zones; they define where datum simulation contacts the part.
Inspection Method
Fixture or simulate the part using the specified target contacts, then inspect related features from the datum established by those targets.
Solid and dashed target leader lines can distinguish near-side and far-side target locations on drawings.
Worked Setup: Casting Datum
A rough casting uses three datum targets A1, A2, and A3 to establish datum plane A.
Contact
A1, A2, A3
Three target locations stabilize the primary datum plane.
Simulate
Fixture pads
The part rests on controlled pads rather than an uneven full surface.
Inspect
From datum A
Related tolerances are evaluated after the target datum is established.
The target scheme creates a repeatable datum from controlled contact points.
Comparison Table
| Target Type | Drawing Cue | Simulator |
|---|---|---|
| Point | X mark | Spherical or point contact |
| Line | Located phantom line | Edge or cylindrical pin |
| Area | Size in upper half | Pad or shaped contact |
Notes
Point targets are often shown with an X-shaped mark at a dimensioned location.
Area targets include size or shape information in the upper half of the target symbol.