Hi Mike, usually the long vertical ones would be used as the rails.

> In Rhino they term it Sweep 2

It sounds like you've got it figured out already, but just in case - in MoI both of Rhino's "Sweep1" and "Sweep2" commands are combined in a single Sweep command, which will do a "Sweep1" if you select just one rail at the rail picking stage, or "Sweep2" if you select 2 rails at the rail picking stage. If you select 3 or more rails MoI will do a sweep1 along each of them.

You can also use Construct > Network on a curve setup like that as well.

- Michael