What is the difference between datum feature symbol and datum target symbol?

What is the difference between datum feature symbol and datum target symbol?

• A. Datum feature symbol identifies which feature provides the datum; datum target marks the precise point or region used to establish the datum
• B. Datum feature symbol marks the datum target
• C. Datum target indicates tolerance zone shape
• D. Datum feature symbol defines material condition

Answer: (A)

The essential idea is that datums are defined by two related pieces of information: which feature provides the datum, and where on that feature the datum is actually established. The datum feature symbol identifies the physical feature on the part that will act as the datum reference. It points to a specific surface, edge, hole, etc., and designates that feature as contributing the datum for the datum reference frame. The datum target symbol is the marker that shows the exact point or region on that feature that is used to establish the datum in practice. It tells you where the inspection setup will touch or measure to locate the datum, which is especially important when the datum is defined by a region rather than a single point. So, the datum feature symbol answers “which feature is the datum coming from?” while the datum target symbol answers “where on that feature is the datum established?” The targets do not define the tolerance zone or material condition themselves; those aspects live in the tolerance frame and its modifiers.

The essential idea is that datums are defined by two related pieces of information: which feature provides the datum, and where on that feature the datum is actually established.

The datum feature symbol identifies the physical feature on the part that will act as the datum reference. It points to a specific surface, edge, hole, etc., and designates that feature as contributing the datum for the datum reference frame.

The datum target symbol is the marker that shows the exact point or region on that feature that is used to establish the datum in practice. It tells you where the inspection setup will touch or measure to locate the datum, which is especially important when the datum is defined by a region rather than a single point.

So, the datum feature symbol answers “which feature is the datum coming from?” while the datum target symbol answers “where on that feature is the datum established?” The targets do not define the tolerance zone or material condition themselves; those aspects live in the tolerance frame and its modifiers.