How is a datum target used?

How is a datum target used?

• A. It defines the exact center of a hole.
• B. It defines a datum on a surface when the datum surface cannot be measured directly.
• C. It sets the maximum material condition.
• D. It indicates the true position.

Answer: (B)

A datum target is used to define a datum on a surface when that surface cannot be measured directly. Datums provide the reference frame for all GD&T tolerances, so if the actual datum surface is inaccessible, deformed, or non-flat, a datum target gives defined points or regions on that surface that can be measured to establish the datum’s location and orientation. In practice, probes or styluses touch the target areas, and the measured coordinates determine the implied plane, line, or point that serves as the datum reference. This lets the true positional and orientation requirements be evaluated against a consistent reference even when the surface itself isn’t directly measurable. Other ideas don’t fit because a datum target isn’t about locating the exact center of a hole or about setting a maximum material condition; those relate to different GD&T concepts. And a datum target isn’t something that indicates true position by itself—it provides a means to establish the datum frame that true-position tolerances will reference.

A datum target is used to define a datum on a surface when that surface cannot be measured directly. Datums provide the reference frame for all GD&T tolerances, so if the actual datum surface is inaccessible, deformed, or non-flat, a datum target gives defined points or regions on that surface that can be measured to establish the datum’s location and orientation. In practice, probes or styluses touch the target areas, and the measured coordinates determine the implied plane, line, or point that serves as the datum reference. This lets the true positional and orientation requirements be evaluated against a consistent reference even when the surface itself isn’t directly measurable.

Other ideas don’t fit because a datum target isn’t about locating the exact center of a hole or about setting a maximum material condition; those relate to different GD&T concepts. And a datum target isn’t something that indicates true position by itself—it provides a means to establish the datum frame that true-position tolerances will reference.