When you first start the Shaft Generator, the shaft contains some sections by default. You design the shaft by modifying, deleting, and adding shaft sections.
You can select the shaft sections with the 2D preview in the dialog box, the graphics window, or with the tree control.
Notice that this section highlights in the 2D preview and in the graphics window.
The first Cylinder section becomes red in the tree control. The Shaft Generator recognizes that you have a fillet between two sections of the same width next to each other, which is not supported. The program changes the section back to the default color when you change the width of one of the shaft sections.