Similar to the cable window there is a window for tubes. It is reached via the menu Tubes | Edit. It is easier because there is only one type of tubes.

Tubes match the tube type bars, but they are considered as separate objects.

For example, I can modify a tube type bar to cable type bar and the bar does not disappear but the tube does.

For comments on the use of this window, see the aforementioned menu Tubes | Edit.

To update the database of the tubes that can be used see section Introduction | Objects | Tubes.