About Creating Asynchronous Datum Features
You need to use datum features as geometric references when you create or edit the definition of features. Examples of datum features are planes, points, axes, curves, or coordinate systems. You can select existing datum features of the model as the reference datum features, or create these reference datum features while you create or edit the definition of the feature. Use the commands in the Model tab Datum group and the relevant geometry as references to create the reference datum features while the feature-creation tool for the main feature is open.
The datum features that are created asynchronously while you create or edit the definition of a feature may or may not be used as references by the feature that you create or edit its definition. When used as references by the feature, the asynchronous datum features are automatically embedded in the feature and are displayed as sub-nodes of the feature on the Model Tree when the creation or the redefinition of the feature is complete. They are automatically hidden after their creation. To view them in the graphics window, you must use 
Unhide on the shortcut menu, or click > Unhide, or View, click the arrow next to Unhide, and then click 
Unhide All.
Unhide on the shortcut menu, or click > Unhide, or View, click the arrow next to Unhide, and then click Unhide All. | In addition to the asynchronous datum features, a feature can also consist of regular internal datum features, such as datum axes and datum planes, as references. Regular datum features are internally created during the creation of certain features, such as a hole, extrude, revolve, or a sketch-based feature. They are automatically created when the corresponding geometry is referenced, but they are not embedded in the features that use them as references. |
Asynchronous datums are not internal to a feature like some regular datum features that are internal to a feature. You can, therefore, drag and drop asynchronous datums outside the main feature in which they are embedded. You can also drag and drop an existing datum feature that was created before the feature into the feature if the feature references the datum features. Another embedded datum of the same feature or a feature of another model also can reference the asynchronous datums embedded in the main feature. Asynchronous datum features that are not used by a feature, and asynchronous datum features that are used by several features, but are not datums of the feature, are not embedded.
An asynchronous datum is not intrinsic to the feature. You can delete, edit, or redefine its definition, references, dimensions, or constraints. Regular datum features are intrinsic to the feature and you cannot delete or redefine the feature to change its constraints, though you can edit its dimensions and references.