To Turn On or Off Snapping to Elements in a Reference

Do one of the following:

In the References dialog's list box, click the Snap column of the entry for the model.
From the References dialog's Properties menu, choose Attachment. The Attachment Properties dialog opens for the selected reference. Turn the Snap check box off or on.
In the References dialog's list box, double-click the reference. The Attachment Properties dialog opens for the selected reference. Turn the Snap check box off or on.