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This script creates ducting pipes from edges in selected group(s)/component(s), also adding fittings to vertices. 
Requirements:
- Windows OS 10 or newer (Some Mac user can use but I didn't test it)
- SketchUp 2019 or newer.
Usage: 
- "Build Rectangle Duct Branch":  All inside edges of selected group(s)/component(s) will be turned to rectangle ducting pipe with options the WxH size can be input in an input box.
- "Build Round Duct Branch":  All inside edges of selected group(s)/component(s) will be turned into rectangle ducting pipe with options the Diameter size can be input in an input box.
- "Edit Fitting": A tool that helps to edit fittings. Click to an ending to install the reduced bush, Shift-Click to install the transition (only from rectangle to round). Click to a reduced/transition to adjust/replace. Click to the whole branch to enter the "edit paths" mode. The edit mode will switch back the branch to the beginning proxy with only edges. After user finishes the edit and closes the group, the plugin will re-create the branch.