Insert a round, rectangular or oblong sink
This article is part of a TARGET 3001! Crash Course Frontpanel.
After clicking the icon 
the following dialog appears:
Image 1: The dialog for placement of a flat milling (sink)
With a flat milling you do not have a break through the material. The tool penetrates only partly into the materialso that a "material background" remains. With a flat milling you can not penetrate deeper than the thickness of the material itself.
Image 2: A 40 mil (1.02 mm) flat milling