The Intersect tool () takes two or more overlapping solid entities and removes all associated geometry except where those solids intersect. In SketchUp for iPad, the Intersect tool does not have any optional tool modes.
iPad Input Methods for the Intersect Tool
The Intersect tool can be used with any of SketchUp for iPad's input methods in either Just Draw or Click-Move-Click mode.
Click-Move-Click Mode or Just Draw Mode
Mouse or Trackpad - Select the Intersect tool and click your first solid. Clicking another solid removes all geometry from those solids except for the intersecting geometry. Repeat for each additional solid you would like to include.
Pencil or Multitouch - Select the Intersect tool and tap your first solid. Tapping another solid removes all geometry from those solids except for the intersecting geometry. Repeat for each additional solid you would like to include.
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For more information on how to use the Outer Shell tool in your models, see Leaving only the intersection geometry in Modeling Complex 3D Shapes with the Solid Tools.