What visually defines the datum plane, axis, or centerplane of a feature?

The datum identification symbol is key in visually defining the datum plane, axis, or centerplane of a feature in geometric dimensioning and tolerancing (GD&T). This symbol indicates the reference point or the starting basis from which measurements are made. Datums establish a frame of reference for locating and orienting features on a part, which is crucial for ensuring proper assembly and function in the final product.

By utilizing specific symbols that clearly denote these datums, designers and engineers communicate precise instructions on how parts should be measured and checked during manufacturing and inspection processes. This clarity helps prevent misunderstandings that could lead to assembly errors or part nonconformance.

While geometric control symbols denote specific forms of tolerance applied to features, inspection marks serve primarily as indicators for inspection points without defining a datum. Similarly, measurement indicators may represent tools or methods used for measurement but do not provide the fundamental reference that a datum identification symbol does.