References create dimensions used to position the library feature (*.sldlfp) on the model (*.sldprt).

To create a library feature that includes references, you need to dimension the library feature relative to the base part on which you create it.

Library features with face references such as fillets do not need reference dimensions.

You can also create references using relations. For example, if you align the center of an arc horizontally, vertically, or coincident to the sketch origin, a reference is created.