Hi Bob, yup if you want to use boolean union you will want to form the various pieces as solids, since the booleans are oriented towards working on solids.

It can sometimes not be quite as easy to make each piece a solid though, particularly if the end profiles of your shapes are not planar - the end cap option in the various surfacing commands like extrude, sweep, loft, only know how to automatically cap planar ends.

So if it is not easy to make the connector piece as a solid, then you can use the other technique that I described above where you can glue 2 surfaces that touch each other along an edge using the Join command. If you're using this technique then that's when you would delete any end caps because the Join command joins together open edges that are not already attached to something.

Does that make sense?

Working with solids at each stage can often be a convenient way to do things though, so yes if you plan to use boolean operations to combine things together you'll want to form each piece as a solid meaning having the end cap option enabled when you create each piece.

- Michael