Select Tools > Thin Parts Attribute... .
The Thin Parts Attribute Definition dialog box appears.

In the Surface box, select the surface.
Choose the input values for Thickness 1 (indicated by the
arrow) and Thickness 2 using the arrows.

You can click the Reverse Direction button to inverse the
direction of thickness 1 and 2.
Click OK to apply the thickness.
Thicknesses 1 and 2 appear in the specification tree, as the
surface's attributes.
